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In git-log we leave the save_commit_buffer flag set to "1", which tells
the commit parsing code to store the object content after it has parsed
it to find parents, tree, etc. That lets us reuse the contents for
pretty-printing the commit in the output. And then after printing each
commit, we call free_commit_buffer(), since we don't need it anymore.
But some options may cause us to traverse commits which are not part of
the output. And so git-log does not see them at all, and doesn't free
them. One such case is something like:
git log -n 1000 --skip=1000000
which will churn through a million commits, before showing only a
thousand. We loop through these inside get_revision(), without freeing
the contents. As a result, we end up storing the object data for those
million commits simultaneously.
We should free the stored buffers (if any) for those commits as we skip
over them, which is what this patch does. Running the above command in
linux.git drops the peak heap usage from ~1.1GB to ~200MB, according to
valgrind/massif. (I thought we might get an even bigger improvement, but
the remaining memory is going to commit/tree structs, which we do hold
on to forever).
Note that this problem doesn't occur if:
- you're running a git-rev-list without a --format parameter; it turns
off save_commit_buffer by default, since it only output the object
id
- you've built a commit-graph file, since in that case we'd use the
optimized graph data instead of the initial parse, and then do a
lazy parse for commits we're actually going to output
There are probably some other option combinations that can likewise
end up with useless stored commit buffers. For example, if you ask for
"foo..bar", then we'll have to walk down to the merge base, and
everything on the "foo" side won't be shown. Tuning the "save" behavior
to handle that might be tricky (I guess maybe drop buffers for anything
we mark as UNINTERESTING?). And in the long run, the right solution here
is probably to make sure the commit-graph is built (since it fixes the
memory problem _and_ drastically reduces CPU usage).
But since this "--skip" case is an easy one-liner, it's worth fixing in
the meantime. It should be OK to make this call even if there is no
saved buffer (e.g., because save_commit_buffer=0, or because a
commit-graph was used), since it's O(1) to look up the buffer and is a
noop if it isn't present. I verified by running the above command after
"git commit-graph write --reachable", and it takes the same time with
and without this patch.
Reported-by: Yuri Karnilaev <karnilaev@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git - fast, scalable, distributed revision control system
Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.
Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.
See Documentation/gittutorial.txt to get started, then see
Documentation/giteveryday.txt for a useful minimum set of commands, and
Documentation/git-<commandname>.txt for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with man gittutorial or git help tutorial, and the
documentation of each command with man git-<commandname> or git help <commandname>.
CVS users may also want to read Documentation/gitcvs-migration.txt
(man gitcvs-migration or git help cvs-migration if git is
installed).
The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission and Documentation/CodingGuidelines).
Those wishing to help with error message, usage and informational message
string translations (localization l10) should see po/README.md
(a po file is a Portable Object file that holds the translations).
To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org (not the Git list). The mailing list archives are available at https://lore.kernel.org/git/, http://marc.info/?l=git and other archival sites.
Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.
The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.
The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (depending on your mood):
- random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant.
- stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
- "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks