On Thu, Mar 01 2018, Nguyễn Thái Ngọc Duy jotted: > The array of object_entry in pack-objects can take a lot of memory > when pack-objects is run in "pack everything" mode. On linux-2.6.git, > this array alone takes roughly 800MB. > > This series reorders some fields and reduces field size... to keep > this struct smaller. Its size goes from 136 bytes to 96 bytes (29%) on > 64-bit linux and saves 260MB on linux-2.6.git. I'm very interested in this patch series. I don't have time to test this one right now (have to run), but with your previous RFC patch memory use (in the ~4GB range) on a big in-house repo went down by a bit over 3%, and it's ~5% faster. Before/after RSS 4440812 / 4290000 & runtime 172.73 / 162.45. This is after having already done a full git gc before, data via /usr/bin/time -v. So not huge, but respectable. We have a big repo, and this gets repacked on 6-8GB of memory on dev KVMs, so we're under a fair bit of memory pressure. git-gc slows things down a lot. It would be really nice to have something that made it use drastically less memory at the cost of less efficient packs. Is the property that you need to spend give or take the size of .git/objects in memory something inherent, or just a limitation of the current implementation? I.e. could we do a first pass to pick some objects based on some heuristic, then repack them N at a time, and finally delete the now-obsolete packs? Another thing I've dealt with is that on these machines their NFS-mounted storage gets exhausted (I'm told) due to some pathological operations git does during repack, I/O tends to get 5-6x slower. Of course ionice doesn't help because the local kernel doesn't know anything about how harmful it is.
