When the number of open packs exceeds pack_max_fds, unuse_one_window()
is called repeatedly to attempt to release the least-recently-used
pack windows, which, as a side-effect, will also close a pack file
after closing its last open window. If a pack file has been opened,
but no windows have been allocated into it, it will never be selected
by unuse_one_window() and hence its file descriptor will not be
closed. When this happens, git may exceed the number of file
descriptors permitted by the system.
This latter situation can occur in show-ref or receive-pack during ref
advertisement. During ref advertisement, receive-pack will iterate
over every ref in the repository and advertise it to the client after
ensuring that the ref exists in the local repository. If the ref is
located inside a pack, then the pack is opened to ensure that it
exists, but since the object is not actually read from the pack, no
mmap windows are allocated. When the number of open packs exceeds
pack_max_fds, unuse_one_window() will not be able to find any windows to
free and will not be able to close any packs. Once the per-process
file descriptor limit is exceeded, receive-pack will produce a warning,
not an error, for each pack it cannot open, and will then most likely
fail with an error to spawn rev-list or index-pack like:
error: cannot create standard input pipe for rev-list: Too many open files
error: Could not run 'git rev-list'
This may also occur during upload-pack when refs are packed (in the
packed-refs file) and the number of packs that must be opened to
verify that these packed refs exist exceeds the file descriptor
limit. If the refs are loose, then upload-pack will read each ref
from the object database (if the object is in a pack, allocating one
or more mmap windows for it) in order to peel tags and advertise the
underlying object. But when the refs are packed and peeled,
upload-pack will use the peeled sha1 in the packed-refs file and
will not need to read from the pack files, so no mmap windows will
be allocated and just like with receive-pack, unuse_one_window()
will never select these opened packs to close.
When we have file descriptor pressure, we just need to find an open
pack to close. We can leave the existing mmap windows open. If
additional windows need to be mapped into the pack file, it will be
reopened when necessary. If the pack file has been rewritten in the
mean time, open_packed_git_1() should notice when it compares the file
size or the pack's sha1 checksum to what was previously read from the
pack index, and reject it.
Let's introduce a new function close_one_pack() designed specifically
for this purpose to search for and close the least-recently-used pack,
where LRU is defined as (in order of preference):
* pack with oldest mtime and no allocated mmap windows
* pack with the least-recently-used windows, i.e. the pack
with the oldest most-recently-used window, where none of
the windows are in use
* pack with the least-recently-used windows
Signed-off-by: Brandon Casey <drafnel@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
////////////////////////////////////////////////////////////////
Git - the stupid content tracker
////////////////////////////////////////////////////////////////
"git" can mean anything, 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
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.
See Documentation/gittutorial.txt to get started, then see
Documentation/everyday.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).
Many Git online resources are accessible from http://git-scm.com/
including full documentation and Git related tools.
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).
To subscribe to the list, send an email with just "subscribe git" in
the body to majordomo@vger.kernel.org. The mailing list archives are
available at http://news.gmane.org/gmane.comp.version-control.git/,
http://marc.info/?l=git and other archival sites.
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.
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