From: Michael Haggerty <mhagger@alum•mit.edu>
To: David Aguilar <davvid@gmail•com>
Cc: Junio C Hamano <gitster@pobox•com>,
Jiang Xin <worldhello.net@gmail•com>,
Lea Wiemann <lewiemann@gmail•com>,
David Reiss <dreiss@facebook•com>, Johannes Sixt <j6t@kdbg•org>,
git@vger•kernel.org, "Lars R. Damerow" <lars@pixar•com>,
Jeff King <peff@peff•net>,
Marc Jordan <marc.jordan@disneyanimation•com>
Subject: Re: [PATCH v3 0/8] Fix GIT_CEILING_DIRECTORIES that contain symlinks
Date: Mon, 29 Oct 2012 06:10:04 +0100 [thread overview]
Message-ID: <508E0FAC.5050600@alum.mit.edu> (raw)
In-Reply-To: <CAJDDKr4ki+NjSeuZpAU6bM=YAQ_3mdHCtawstdCqe9Ewvp=arQ@mail.gmail.com>
On 10/29/2012 01:15 AM, David Aguilar wrote:
> On Sat, Oct 20, 2012 at 11:51 PM, Junio C Hamano <gitster@pobox•com> wrote:
>> Michael Haggerty <mhagger@alum•mit.edu> writes:
>>
>>> This patch series has the side effect that all of the directories
>>> listed in GIT_CEILING_DIRECTORIES are accessed *unconditionally* to
>>> resolve any symlinks that are present in their paths. It is
>>> admittedly odd that a feature intended to avoid accessing expensive
>>> directories would now *intentionally* access directories near the
>>> expensive ones. In the above scenario this shouldn't be a problem,
>>> because /home would be the directory listed in
>>> GIT_CEILING_DIRECTORIES, and accessing /home itself shouldn't be
>>> expensive.
>>
>> Interesting observation. In the last sentence, "accessing /home"
>> does not exactly mean accessing /home, but accessing / to learn
>> about "home" in it, no?
>>
>>> But there might be other scenarios for which this patch
>>> series causes a performance regression.
>>
>> Yeah, after merging this to 'next', we should ask people who care
>> about CEILING to test it sufficiently.
>>
>> Thanks for rerolling.
>
> GIT_CEILING_DIRECTORIES was always about trying to avoid
> hitting them at all; they can be (busy) NFS volumes there.
>
> Here's the description from the 1.6.0 release notes:
>
> * A new environment variable GIT_CEILING_DIRECTORIES can be used to stop
> the discovery process of the toplevel of working tree; this may be useful
> when you are working in a slow network disk and are outside any working tree,
> as bash-completion and "git help" may still need to run in these places.
>
> In 8030e44215fe8f34edd57d711a35f2f0f97a0423 Lars added
> GIT_ONE_FILESYSTEM to fix a related issue.
> Do you guys have GIT_CEILING_DIRECTORIES set too?
>
> We use GIT_CEILING_DIRECTORIES and I'm pretty sure
> we don't want every git command hitting them, so this would
> be a regression when seen from the POV of our current usage
> of this variable, which would be a bummer.
I would certainly withdraw the patch series if it causes a performance hit.
The log message of the original commit (0454dd93bf) described the
following scenario: a /home partition under which user home directories
are automounted, and setting GIT_CEILING_DIRECTORIES=/home to avoid
hitting /home/.git, /home/.git/objects, and /home/objects (which would
attempt to automount those directories). I believe that this scenario
would not be slowed down by my patches.
How do you use GIT_CEILING_DIRECTORIES that the proposed changes cause a
slowdown?
> Is there another way to accomplish this without the performance hit?
> Maybe something that can be solved with configuration?
Without doing the symlink expansion there is no way for git to detect
that GIT_CEILING_DIRECTORIES contains symlinks and is therefore
ineffective. So the user has no warning about the misconfiguration
(except that git runs slowly).
On 10/29/2012 02:42 AM, Junio C Hamano wrote:
> Perhaps not canonicalize elements on the CEILING list ourselves? If
> we make it a user error to put symlinked alias in the variable, and
> document it clearly, wouldn't it suffice?
There may be no other choice. (That, and fix the test suite in another
way to tolerate a $PWD that involves symlinks.)
Michael
--
Michael Haggerty
mhagger@alum•mit.edu
http://softwareswirl.blogspot.com/
next prev parent reply other threads:[~2012-10-29 5:10 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-21 5:57 [PATCH v3 0/8] Fix GIT_CEILING_DIRECTORIES that contain symlinks Michael Haggerty
2012-10-21 5:57 ` [PATCH v3 1/8] Introduce new static function real_path_internal() Michael Haggerty
2012-10-21 5:57 ` [PATCH v3 2/8] real_path_internal(): add comment explaining use of cwd Michael Haggerty
2012-10-21 5:57 ` [PATCH v3 3/8] Introduce new function real_path_if_valid() Michael Haggerty
2012-10-21 5:57 ` [PATCH v3 4/8] longest_ancestor_length(): use string_list_split() Michael Haggerty
2012-10-21 5:57 ` [PATCH v3 5/8] longest_ancestor_length(): take a string_list argument for prefixes Michael Haggerty
2012-10-21 5:57 ` [PATCH v3 6/8] longest_ancestor_length(): require prefix list entries to be normalized Michael Haggerty
2012-10-22 20:04 ` Johannes Sixt
2012-10-21 5:57 ` [PATCH v3 7/8] normalize_ceiling_entry(): resolve symlinks Michael Haggerty
2012-10-21 5:57 ` [PATCH v3 8/8] string_list_longest_prefix(): remove function Michael Haggerty
2012-10-21 6:51 ` [PATCH v3 0/8] Fix GIT_CEILING_DIRECTORIES that contain symlinks Junio C Hamano
2012-10-22 8:26 ` Michael Haggerty
2012-10-29 0:15 ` David Aguilar
2012-10-29 1:42 ` Junio C Hamano
2012-10-29 5:10 ` Michael Haggerty [this message]
2012-11-12 17:47 ` Junio C Hamano
2012-11-13 20:50 ` David Aguilar
2012-11-15 8:18 ` Michael Haggerty
2013-02-20 6:20 ` Anders Kaseorg
2013-02-20 6:55 ` Junio C Hamano
2013-02-20 9:09 ` [RFC] Provide a mechanism to turn off symlink resolution in ceiling paths Michael Haggerty
2013-02-20 17:41 ` Junio C Hamano
2013-02-21 22:53 ` Junio C Hamano
2013-02-22 7:23 ` Michael Haggerty
2013-02-20 9:39 ` [PATCH v3 0/8] Fix GIT_CEILING_DIRECTORIES that contain symlinks Anders Kaseorg
2012-10-29 5:34 ` Lars Damerow
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