Are there any fundamenta lobjections to the patchset? I plan to resubmit next week with the changes from the feedback along with the mmap_sem down_write_killable usage.
On Tue 02-02-16 21:19:17, Michal Hocko wrote: > Hi, > the following patchset implements a killable variant of write lock for > rw_semaphore. My usecase is to turn as many mmap_sem write users to use > a killable variant which will be helpful for the oom_reaper [1] to > asynchronously tear down the oom victim address space which requires > mmap_sem for read. This will reduce a likelihood of OOM livelocks caused > by oom victim being stuck on a lock or other resource which prevents it > to reach its exit path and release the memory. I haven't implemented > the killable variant of the read lock because I do not have any usecase > for this API. > > The patchset is organized as follows. > - Patch 1 is a trivial cleanup > - Patch 2, I belive, shouldn't introduce any functional changes as per > Documentation/memory-barriers.txt. > - Patch 3 is the preparatory work and necessary infrastructure for > down_write_killable. It implements generic __down_write_killable > and prepares the write lock slow path to bail out earlier when told so > - Patch 4-9 are implementing arch specific __down_write_killable. One > patch per architecture. I haven't even tried to compile test anything but > sparch which uses CONFIG_RWSEM_GENERIC_SPINLOCK in allnoconfig. > Those shold be mostly trivial. > - One exception is x86 which replaces the current implementation of > __down_write with the generic one to make easier to read and get rid > of one level of indirection to the slow path. More on that in patch 10. > I do not have any problems to drop patch 10 and rework 11 to the current > inline asm but I think the easier code would be better. > - finally patch 11 implements down_write_killable and ties everything > together. I am not really an expert on lockdep so I hope I got it right. > > Many of arch specific patches are basically same and I can squash them > into one patch if this is preferred but I thought that one patch per > arch is preferable. > > My patch to change mmap_sem write users to killable form is not part > of the series because it is not finished yet but I guess it is not > really necessary for the RFC. The API is used in the same way as > mutex_lock_killable. > > I have tested on x86 with OOM situations with high mmap_sem contention > (basically many parallel page faults racing with many parallel mmap/munmap > tight loops) so the waiters for the write locks are routinely interrupted > by SIGKILL. > > Patches should apply cleanly on both Linus and next tree. > > Any feedback is highly appreciated. > --- > [1] http://lkml.kernel.org/r/1452094975-551-1-git-send-email-mho...@kernel.org -- Michal Hocko SUSE Labs
