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: __alloc_pages_direct_compact(): ... current->flags |= PF_MEMALLOC; *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac, prio); current->flags &= ~PF_MEMALLOC; And later in __alloc_pages_slowpath(): /* Avoid recursion of direct reclaim */ if (current->flags & PF_MEMALLOC) <=== false goto nopage; /* Try direct reclaim and then allocating */ page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags, ac, &did_some_progress); -- 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>
