Re: [PATCH v3 0/8] Fix GIT_CEILING_DIRECTORIES that contain symlinks

[Michael Haggerty <mhagger@alum.mit.edu>]

On 10/21/2012 08:51 AM, Junio C Hamano 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?

This is the extra overhead on my system for using
GIT_CEILING_DIRECTORIES=/home:

stat("/home", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
getcwd("/home/mhagger", 1024)           = 14
chdir("/home")                          = 0
getcwd("/home", 4096)                   = 6
lstat("/home", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
chdir("/home/mhagger")                  = 0

If I use GIT_CEILING_DIRECTORIES=/dev/shm, which is a symlink to
/run/shm on my system, the overhead is comparable:

stat("/dev/shm", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=200, ...}) = 0
getcwd("/home/mhagger", 1024)           = 14
chdir("/dev/shm")                       = 0
getcwd("/run/shm", 4096)                = 9
lstat("/run/shm", {st_mode=S_IFDIR|S_ISVTX|0777, st_size=200, ...}) = 0
chdir("/home/mhagger")                  = 0

Michael

-- 
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/