Commit Graph

147 Commits

Author SHA1 Message Date
Junio C Hamano
c0b48ad777 Merge branch 'np/verify-pack'
* np/verify-pack:
  add storage size output to 'git verify-pack -v'
  fix unimplemented packed_object_info_detail() features
  make verify_one_pack() a bit less wrong wrt packed_git structure
  factorize revindex code out of builtin-pack-objects.c

Conflicts:

	Makefile
2008-03-02 16:07:30 -08:00
Junio C Hamano
eadbcd498a Merge branch 'mk/maint-parse-careful'
* mk/maint-parse-careful:
  receive-pack: use strict mode for unpacking objects
  index-pack: introduce checking mode
  unpack-objects: prevent writing of inconsistent objects
  unpack-object: cache for non written objects
  add common fsck error printing function
  builtin-fsck: move common object checking code to fsck.c
  builtin-fsck: reports missing parent commits
  Remove unused object-ref code
  builtin-fsck: move away from object-refs to fsck_walk
  add generic, type aware object chain walker

Conflicts:

	Makefile
	builtin-fsck.c
2008-03-02 15:11:07 -08:00
Nicolas Pitre
3449f8c4cb factorize revindex code out of builtin-pack-objects.c
No functional change. This is needed to fix verify-pack in a later patch.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-03-01 01:44:45 -08:00
Junio C Hamano
3d0a936f63 Merge branch 'jm/free'
* jm/free:
  Avoid unnecessary "if-before-free" tests.

Conflicts:

	builtin-branch.c
2008-02-27 13:03:50 -08:00
Junio C Hamano
392b78ca42 Revert "pack-objects: Print a message describing the number of threads for packing"
This reverts commit 6c723f5e6b.
The additional message may be interesting for git developers,
but not useful for the end users, and clutters the output.
2008-02-26 23:27:31 -08:00
Martin Koegler
7914053ba9 Remove unused object-ref code
Signed-off-by: Martin Koegler <mkoegler@auto.tuwien.ac.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-02-25 23:57:35 -08:00
Brandon Casey
6c723f5e6b pack-objects: Print a message describing the number of threads for packing
Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-02-23 12:00:32 -08:00
Andreas Ericsson
833e3df171 pack-objects: Add runtime detection of online CPU's
Packing objects can be done in parallell nowadays, but it's
only done if the config option pack.threads is set to a value
above 1. Because of that, the code-path used is often not the
most optimal one.

This patch adds a routine to detect the number of online CPU's
at runtime (online_cpus()). When pack.threads (or --threads=) is
given a value of 0, the number of threads is set to the number of
online CPU's. This feature is also documented.

As per Nicolas Pitre's recommendations, the default is still to
run pack-objects single-threaded unless explicitly activated,
either by configuration or by command line parameter.

The routine online_cpus() is a rework of "numcpus.c", written by
one Philip Willoughby <pgw99@doc.ic.ac.uk>. numcpus.c is in the
public domain and can presently be downloaded from
http://csgsoft.doc.ic.ac.uk/numcpus/

Signed-off-by: Andreas Ericsson <ae@op5.se>
Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-02-23 12:00:32 -08:00
Jim Meyering
8e0f70033b Avoid unnecessary "if-before-free" tests.
This change removes all obvious useless if-before-free tests.
E.g., it replaces code like this:

        if (some_expression)
                free (some_expression);

with the now-equivalent:

        free (some_expression);

It is equivalent not just because POSIX has required free(NULL)
to work for a long time, but simply because it has worked for
so long that no reasonable porting target fails the test.
Here's some evidence from nearly 1.5 years ago:

    http://www.winehq.org/pipermail/wine-patches/2006-October/031544.html

FYI, the change below was prepared by running the following:

  git ls-files -z | xargs -0 \
  perl -0x3b -pi -e \
    's/\bif\s*\(\s*(\S+?)(?:\s*!=\s*NULL)?\s*\)\s+(free\s*\(\s*\1\s*\))/$2/s'

Note however, that it doesn't handle brace-enclosed blocks like
"if (x) { free (x); }".  But that's ok, since there were none like
that in git sources.

Beware: if you do use the above snippet, note that it can
produce syntactically invalid C code.  That happens when the
affected "if"-statement has a matching "else".
E.g., it would transform this

  if (x)
    free (x);
  else
    foo ();

into this:

  free (x);
  else
    foo ();

There were none of those here, either.

If you're interested in automating detection of the useless
tests, you might like the useless-if-before-free script in gnulib:
[it *does* detect brace-enclosed free statements, and has a --name=S
 option to make it detect free-like functions with different names]

  http://git.sv.gnu.org/gitweb/?p=gnulib.git;a=blob;f=build-aux/useless-if-before-free

Addendum:
  Remove one more (in imap-send.c), spotted by Jean-Luc Herren <jlh@gmx.ch>.

Signed-off-by: Jim Meyering <meyering@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-02-22 14:14:40 -08:00
Martin Koegler
3d51e1b5b8 check return code of prepare_revision_walk
A failure in prepare_revision_walk can be caused by
a not parseable object.

Signed-off-by: Martin Koegler <mkoegler@auto.tuwien.ac.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-02-17 23:51:12 -08:00
Junio C Hamano
aa8d53ec38 Merge branch 'maint'
* maint:
  config: add test cases for empty value and no value config variables.
  cvsimport: have default merge regex also match beginning of commit message
  git clone -s documentation: force a new paragraph for the NOTE
  status: suggest "git rm --cached" to unstage for initial commit
  Protect get_author_ident_from_commit() from filenames in work tree
  upload-pack: Initialize the exec-path.
  bisect: use verbatim commit subject in the bisect log
  git-cvsimport.txt: fix '-M' description.
  Revert "pack-objects: only throw away data during memory pressure"
2008-02-13 14:33:19 -08:00
Junio C Hamano
75ad235c2e Revert "pack-objects: only throw away data during memory pressure"
This reverts commit 9c2174350c.

Nico analyzed and found out that this does not really help, and
I agree with it.

By the time this gets into action and data is actively thrown
away, performance simply goes down the drain due to the data
constantly being reloaded over and over and over and over and
over and over again, to the point of virtually making no
relative progress at all.  The previous behavior of enforcing
the memory limit by dynamically shrinking the window size at
least had the effect of allowing some kind of progress, even if
the end result wouldn't be optimal.

And that's the whole point behind this memory limiting feature:
allowing some progress to be made when resources are too limited
to let the repack go unbounded.
2008-02-12 23:39:03 -08:00
Junio C Hamano
04f32cf1b3 Merge branch 'maint'
* maint: (35 commits)
  config.c: guard config parser from value=NULL
  builtin-log.c: guard config parser from value=NULL
  imap-send.c: guard config parser from value=NULL
  wt-status.c: guard config parser from value=NULL
  setup.c: guard config parser from value=NULL
  remote.c: guard config parser from value=NULL
  merge-recursive.c: guard config parser from value=NULL
  http.c: guard config parser from value=NULL
  help.c: guard config parser from value=NULL
  git.c: guard config parser from value=NULL
  diff.c: guard config parser from value=NULL
  convert.c: guard config parser from value=NULL
  connect.c: guard config parser from value=NULL
  builtin-tag.c: guard config parser from value=NULL
  builtin-show-branch.c: guard config parser from value=NULL
  builtin-reflog.c: guard config parser from value=NULL
  builtin-log.c: guard config parser from value=NULL
  builtin-config.c: guard config parser from value=NULL
  builtin-commit.c: guard config parser from value=NULL
  builtin-branch.c: guard config parser from value=NULL
  ...
2008-02-11 13:23:06 -08:00
Martin Koegler
9c2174350c pack-objects: only throw away data during memory pressure
If pack-objects hit the memory limit, it deletes objects from the delta
window.

This patch make it only delete the data, which is recomputed, if needed again.

Signed-off-by: Martin Koegler <mkoegler@auto.tuwien.ac.at>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-02-11 12:24:33 -08:00
Johannes Schindelin
2b84b5a874 Introduce the config variable pack.packSizeLimit
"git pack-objects" has the option --max-pack-size to limit the file
size of the packs to a certain amount of bytes.  On platforms where
the pack file size is limited by filesystem constraints, it is easy
to forget this option, and this option does not exist for "git gc"
to begin with.

So introduce a config variable to set the default maximum, but make
this overrideable by the command line.

Suggested by Tor Arvid Lund.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-02-09 23:41:34 -08:00
Nicolas Pitre
6fc74703de pack-objects: Fix segfault when object count is less than thread count
When partitioning the work amongst threads, dividing the number of
objects by the number of threads may return 0 when there are less
objects than threads; this will cause the subsequent code to segfault
when accessing list[sub_size-1].  Allow some threads to have
zero objects to work on instead of barfing, while letting others
to have more.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-01-21 17:24:12 -08:00
Junio C Hamano
8c3c7b2adb pack-objects: remove redundant and wrong call to deflateEnd()
We somehow called deflateEnd() on a stream that we have called
deflateEnd() on already.

In fact, the second deflateEnd() has always been returning
Z_STREAM_ERROR.  We just never checked the error return from
that particular deflateEnd().

The first one returns 0 for success.  We might want to tighten
the check even more to check that.

Noticed by Marco.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-01-10 23:27:39 -08:00
Jim Meyering
872c930dcb Don't access line[-1] for a zero-length "line" from fgets.
A NUL byte at beginning of file, or just after a newline
would provoke an invalid buf[-1] access in a few places.

* builtin-grep.c (cmd_grep): Don't access buf[-1].
* builtin-pack-objects.c (get_object_list): Likewise.
* builtin-rev-list.c (read_revisions_from_stdin): Likewise.
* bundle.c (read_bundle_header): Likewise.
* server-info.c (read_pack_info_file): Likewise.
* transport.c (insert_packed_refs): Likewise.

Signed-off-by: Jim Meyering <meyering@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2008-01-04 12:28:58 -08:00
Johannes Sixt
68e6a4f80d Plug a resource leak in threaded pack-objects code.
A mutex and a condition variable is allocated for each thread and torn
down when the thread terminates. However, for certain workloads it can
happen that some threads are actually not started at all. In this case
we would leak the mutex and condition variable. Now we allocate them only
for those threads that are actually started.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-12-17 16:08:40 -08:00
Johannes Sixt
50f22ada52 threaded pack-objects: Use condition variables for thread communication.
In the threaded pack-objects code the main thread and the worker threads
must mutually signal that they have assigned a new pack of work or have
completed their work, respectively. Previously, the code used mutexes that
were locked in one thread and unlocked from a different thread, which is
bogus (and happens to work on Linux).

Here we rectify the implementation by using condition variables: There is
one condition variable on which the main thread waits until a thread
requests new work; and each worker thread has its own condition variable
on which it waits until it is assigned new work or signaled to terminate.

As a cleanup, the worker threads are spawned only after the initial work
packages have been assigned.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Acked-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-12-16 19:26:12 -08:00
Nicolas Pitre
eb9688ff65 pack-objects: more threaded load balancing fix with often changed paths
The code that splits the object list amongst work threads tries to do so
on "path" boundaries not to prevent good delta matches.  However, in
some cases, a few paths may largely dominate the hash distribution and
it is not possible to have good load balancing without ignoring those
boundaries.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-12-10 17:10:16 -08:00
Nicolas Pitre
384b32c09b pack-objects: fix threaded load balancing
The current method consists of a master thread serving chunks of objects
to work threads when they're done with their previous chunk.  The issue
is to determine the best chunk size: making it too large creates poor
load balancing, while making it too small has a negative effect on pack
size because of the increased number of chunk boundaries and poor delta
window utilization.

This patch implements a completely different approach by initially
splitting the work in large chunks uniformly amongst all threads, and
whenever a thread is done then it steals half of the remaining work from
another thread with the largest amount of unprocessed objects.

This has the advantage of greatly reducing the number of chunk boundaries
with an almost perfect load balancing.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-12-08 03:38:36 -08:00
Nicolas Pitre
b904166ccb pack-objects: reverse the delta search sort list
It is currently sorted and then walked backward.  Not only this doesn't
feel natural for my poor brain, but it would make the next patch less
obvious as well.

So reverse the sort order, and reverse the list walking direction,
which effectively produce the exact same end result as before.

Also bring the relevant comment nearer the actual code and adjust it
accordingly, with minor additional clarifications.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-12-08 03:38:35 -08:00
Nicolas Pitre
b7a28f7827 pack-objects: fix delta cache size accounting
The wrong value was substracted from delta_cache_size when replacing
a cached delta, as trg_entry->delta_size was used after the old size
had been replaced by the new size.

Noticed by Linus.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-12-08 03:38:35 -08:00
Linus Torvalds
4d1012c370 Fix rev-list when showing objects involving submodules
The function mark_tree_uninteresting() assumed that the tree entries
are blob when they are not trees.  This is not so.  Since we do
not traverse into submodules (yet), the gitlinks should be ignored.

In general, we should try to start moving away from using the
"S_ISLNK()" like things for internal git state. It was a mistake to
just assume the numbers all were same across all systems in the first
place.  This implementation converts to the "object_type", and then
uses a case statement.

Noticed by Ilari on IRC.
Test script taken from an earlier version by Dscho.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-11-14 03:44:22 -08:00
Junio C Hamano
e091653951 Merge branch 'np/pack'
* np/pack:
  pack-objects: get rid of an ugly cast
  make the pack index version configurable

Conflicts:

	builtin-pack-objects.c
2007-11-04 01:11:17 -07:00
Nicolas Pitre
79814f425c pack-objects: get rid of an ugly cast
... when calling write_idx_file().

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-11-02 01:41:04 -07:00
Nicolas Pitre
4d00bda2aa make the pack index version configurable
It is a good idea to use pack index version 2 all the time since it has
proper protection against propagation of certain pack corruptions when
repacking which is not possible with index version 1, as demonstrated
in test t5302.

Hence this config option.

The default is still pack index version 1.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-11-02 01:32:02 -07:00
Nicolas Pitre
2a128d63dc add throughput display to git-push
This one triggers only when git-pack-objects is called with
--all-progress and --stdout which is the combination used by
git-push.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-10-30 16:08:40 -07:00
Nicolas Pitre
4d4fcc5451 relax usage of the progress API
Since it is now OK to pass a null pointer to display_progress() and
stop_progress() resulting in a no-op, then we can simplify the code
and remove a bunch of lines by not making those calls conditional all
the time.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-10-30 16:08:40 -07:00
Nicolas Pitre
dc6a0757c4 make struct progress an opaque type
This allows for better management of progress "object" existence,
as well as making the progress display implementation more independent
from its callers.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-10-30 16:08:40 -07:00
Shawn O. Pearce
9c60a966f2 Change 'Deltifying objects' to 'Compressing objects'
Recently I was referred to the Grammar Police as the git-pack-objects
progress message 'Deltifying %u objects' is considered to be not
proper English to at least some small but vocal segment of the
English speaking population.  Techncially we are applying delta
compression to these objects at this stage, so the new term is
slightly more acceptable to the Grammar Police but is also just
as correct.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
2007-10-18 23:34:09 -04:00
Nicolas Pitre
4049b9cfc0 fix const issues with some functions
Two functions, namely write_idx_file() and open_pack_file(), currently
return a const pointer.  However that pointer is either a copy of the
first argument, or set to a malloc'd buffer when that first argument
is null.  In the later case it is wrong to qualify that pointer as const
since ownership of the buffer is transferred to the caller to dispose of,
and obviously the free() function is not meant to be passed const
pointers.

Making the return pointer not const causes a warning when the first
argument is returned since that argument is also marked const.

The correct thing to do is therefore to remove the const qualifiers,
avoiding the need for ugly casts only to silence some warnings.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
2007-10-17 02:54:57 -04:00
Nicolas Pitre
7ba502c47b pack-objects.c: fix some global variable abuse and memory leaks
To keep things well layered, sha1close() now returns the file descriptor
when it doesn't close the file.

An ugly cast was added to the return of write_idx_file() to avoid a
warning.  A proper fix will come separately.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
2007-10-17 02:54:56 -04:00
Nicolas Pitre
2f8b89472c pack-objects: no delta possible with only one object in the list
... so don't even try in that case, and save another useless line of
progress display.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
2007-10-17 02:54:56 -04:00
Nicolas Pitre
42e18fbf5f more compact progress display
Each progress can be on a single line instead of two.

[sp: Changed "Checking files out" to "Checking out files" at
     Johannes Sixt's suggestion as it better explains the
	 action that is taking place]

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
2007-10-17 02:54:55 -04:00
Junio C Hamano
0341091a9e Merge branch 'jc/autogc'
* jc/autogc:
  git-gc --auto: run "repack -A -d -l" as necessary.
  git-gc --auto: restructure the way "repack" command line is built.
  git-gc --auto: protect ourselves from accumulated cruft
  git-gc --auto: add documentation.
  git-gc --auto: move threshold check to need_to_gc() function.
  repack -A -d: use --keep-unreachable when repacking
  pack-objects --keep-unreachable
  Export matches_pack_name() and fix its return value
  Invoke "git gc --auto" from commit, merge, am and rebase.
  Implement git gc --auto
2007-10-03 03:05:32 -07:00
Junio C Hamano
08cdfb1337 pack-objects --keep-unreachable
This new option is meant to be used in conjunction with the
options "git repack -a -d" usually invokes the underlying
pack-objects with.  When this option is given, objects unreachable
from the refs in packs named with --unpacked= option are added
to the resulting pack, in addition to the reachable objects that
are not in packs marked with *.keep files.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-17 12:25:26 -07:00
Junio C Hamano
e1ef867328 builtin-pack-objects.c: avoid bogus gcc warnings
These empty statement marcos can solicit bogus "statement with no effect"
warnings; squelch them.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-14 22:30:20 -07:00
Nicolas Pitre
3c70183918 threaded delta search: proper locking for cache accounting
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-12 12:56:09 -07:00
Nicolas Pitre
693b86fffb threaded delta search: add pack.threads config variable
Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-10 10:50:21 -07:00
Nicolas Pitre
b81d9af71e fix threaded delta search locking
Found by Jeff King.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-10 10:49:11 -07:00
Nicolas Pitre
367f4a4343 threaded delta search: specify number of threads at run time
This adds a --threads=<n> parameter to 'git pack-objects' with
documentation.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-09 22:26:06 -07:00
Nicolas Pitre
59921b4b3f threaded delta search: better chunck split point
Try to keep object with the same name hash together.

Suggested by Martin Koegler.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-09 22:25:43 -07:00
Nicolas Pitre
c2a33679a7 threaded delta search: refine work allocation
With this, each thread get repeatedly assigned the next available chunk of
objects to process until the whole list is done.  The idea is to have
reasonably small chunks so that all CPUs remain busy with a minimum
number of threads for as long as there is data to process.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-09 22:25:33 -07:00
Nicolas Pitre
8ecce684a3 basic threaded delta search
this is still rough, hence it is disabled by default.  You need to compile
with "make THREADED_DELTA_SEARCH=1 ..." at the moment.

Threading is done on different portions of the object list to be
deltified. This is currently done by spliting the list into n parts and
then a thread is spawned for each of them.  A better method would consist
of spliting the list into more smaller parts and have the n threads
pick the next part available.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-06 00:01:45 -07:00
Nicolas Pitre
e334977dfa rearrange delta search progress reporting
This is to help threadification of the delta search code, with a bonus
consistency check.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-06 00:01:44 -07:00
Nicolas Pitre
ef0316fcd9 localize window memory usage accounting
This is to help threadification of delta searching.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-05 23:49:28 -07:00
Nicolas Pitre
75d3985319 straighten the list of objects to deltify
Not all objects are subject to deltification, so avoid carrying those
along, and provide the real count to progress display.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-05 23:49:10 -07:00
Junio C Hamano
776398709d Keep last used delta base in the delta window
This is based on Martin Koegler's idea to keep the object that
was successfully used as the base of the delta when it is about
to fall off the edge of the window.  Instead of doing so only
for the objects at the edge of the window, this makes the window
a lru eviction mechanism.  If an entry is used as a base, it is
moved to the last of the queue to be evicted.

This is a quick-and-dirty implementation, as it keeps the original
implementation of the data structure used for the window.  This
originally was done as an array, not as an array of pointers,
because it was meant to be used as a cyclic FIFO buffer and a
plain array avoids an extra pointer indirection, while its FIFOness
eant that we are not "moving" the entries like this patch does.

The runtime from three versions were comparable.  It seems to
make the resulting chain even shorter, which can only be good.

(stock "master") 15782196 bytes
chain length = 1: 2972 objects
chain length = 2: 2651 objects
chain length = 3: 2369 objects
chain length = 4: 2121 objects
chain length = 5: 1877 objects
...
chain length = 46: 490 objects
chain length = 47: 515 objects
chain length = 48: 527 objects
chain length = 49: 570 objects
chain length = 50: 408 objects

(with your patch) 15745736 bytes (0.23% smaller)
chain length = 1: 3137 objects
chain length = 2: 2688 objects
chain length = 3: 2322 objects
chain length = 4: 2146 objects
chain length = 5: 1824 objects
...
chain length = 46: 503 objects
chain length = 47: 509 objects
chain length = 48: 536 objects
chain length = 49: 588 objects
chain length = 50: 357 objects

(with this patch) 15612086 bytes (1.08% smaller)
chain length = 1: 4831 objects
chain length = 2: 3811 objects
chain length = 3: 2964 objects
chain length = 4: 2352 objects
chain length = 5: 1944 objects
...
chain length = 46: 327 objects
chain length = 47: 353 objects
chain length = 48: 304 objects
chain length = 49: 298 objects
chain length = 50: 135 objects

[jc: this is with code simplification follow-up from Nico]

Signed-off-by: Junio C Hamano <gitster@pobox.com>
2007-09-01 23:53:47 -07:00