On Mon 03-04-17 15:37:07, Andrey Ryabinin wrote: > > > On 04/03/2017 11:47 AM, Michal Hocko wrote: > > On Fri 31-03-17 10:00:30, Shakeel Butt wrote: > >> On Fri, Mar 31, 2017 at 8:30 AM, Andrey Ryabinin > >> <aryabinin@xxxxxxxxxxxxx> wrote: > >>> zswap_frontswap_store() is called during memory reclaim from > >>> __frontswap_store() from swap_writepage() from shrink_page_list(). > >>> This may happen in NOFS context, thus zswap shouldn't use __GFP_FS, > >>> otherwise we may renter into fs code and deadlock. > >>> zswap_frontswap_store() also shouldn't use __GFP_IO to avoid recursion > >>> into itself. > >>> > >> > >> Is it possible to enter fs code (or IO) from zswap_frontswap_store() > >> other than recursive memory reclaim? However recursive memory reclaim > >> is protected through PF_MEMALLOC task flag. The change seems fine but > >> IMHO reasoning needs an update. Adding Michal for expert opinion. > > > > Yes this is true. > > Actually, no. I think we have a bug in allocator which may lead to > recursive direct reclaim. > > E.g. for costly order allocations (or order > 0 && > ac->migratetype != MIGRATE_MOVABLE) with __GFP_NOMEMALLOC > (gfp_pfmemalloc_allowed() returns false) __alloc_pages_slowpath() > may call __alloc_pages_direct_compact() and unconditionally clear > PF_MEMALLOC: Not sure what is the bug here. __GFP_NOMEMALLOC is supposed to inhibit PF_MEMALLOC. And we do not recurse to the reclaim path. We only do the compaction. Or what am I missing? -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
