On Mon 12-08-24 20:59:53, Yafang Shao wrote: > On Mon, Aug 12, 2024 at 7:37 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > > On Mon, Aug 12, 2024 at 05:05:24PM +0800, Yafang Shao wrote: > > > The PF_MEMALLOC_NORECLAIM flag was introduced in commit eab0af905bfc > > > ("mm: introduce PF_MEMALLOC_NORECLAIM, PF_MEMALLOC_NOWARN"). To complement > > > this, let's add two helper functions, memalloc_nowait_{save,restore}, which > > > will be useful in scenarios where we want to avoid waiting for memory > > > reclamation. > > > > No, forcing nowait on callee contets is just asking for trouble. > > Unlike NOIO or NOFS this is incompatible with NOFAIL allocations > > I don’t see any incompatibility in __alloc_pages_slowpath(). The > ~__GFP_DIRECT_RECLAIM flag only ensures that direct reclaim is not > performed, but it doesn’t prevent the allocation of pages from > ALLOC_MIN_RESERVE, correct? Right but this means that you just made any potential nested allocation within the scope that is GFP_NOFAIL a busy loop essentially. Not to mention it BUG_ON as non-sleeping GFP_NOFAIL allocations are unsupported. I believe this is what Christoph had in mind. I am really surprised that we even have PF_MEMALLOC_NORECLAIM in the first place! Unsurprisingly this was merged without any review by the MM community :/ -- Michal Hocko SUSE Labs