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May 23:10, Gao Xiang wrote: > Hi, > > On 2024/5/8 22:43, Hailong Liu wrote: > > On Wed, 08. May 21:41, Gao Xiang wrote: > > > > > > +Cc Michal, > > > > > > On 2024/5/8 20:58, hailong.liu@oppo.com wrote: > > > > From: "Hailong.Liu" > > > > > > > > Commit a421ef303008 ("mm: allow !GFP_KERNEL allocations for kvmalloc") > > > > includes support for __GFP_NOFAIL, but it presents a conflict with > > > > commit dd544141b9eb ("vmalloc: back off when the current task is > > > > OOM-killed"). A possible scenario is as belows: > > > > > > > > process-a > > > > kvcalloc(n, m, GFP_KERNEL | __GFP_NOFAIL) > > > > __vmalloc_node_range() > > > > __vmalloc_area_node() > > > > vm_area_alloc_pages() > > > > --> oom-killer send SIGKILL to process-a > > > > if (fatal_signal_pending(current)) break; > > > > --> return NULL; > > > > > > > > to fix this, do not check fatal_signal_pending() in vm_area_alloc_pages() > > > > if __GFP_NOFAIL set. > > > > > > > > Reported-by: Oven > > > > Signed-off-by: Hailong.Liu > > > > > > Why taging this as RFC here? It seems a corner-case fix of > > > commit a421ef303008 > > > > > > Thanks, > > > Gao Xiang > > > > > > > Hi Gao Xiang: > > > > RFC here to wait for a better way to handle this case :). > > IMO, if vmalloc support __GFP_NOFAIL it should not return > > null even system is deadlock on memory. > > The starting point is that kmalloc doesn't support __GFP_NOFAIL > if order > 1 (even for very short temporary uses), see: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/mm/page_alloc.c?h=v6.8#n2896 > > but it is possible if we have such page pointer array (since two > (order-1) pages can only keep 1024 8-byte entries, it can happen > if compression ratios are high), and kvmalloc(__GFP_NOFAIL) has > already been supported for almost two years, it will fallback to > order-0 allocation as described in commit e9c3cda4d86e > ("mm, vmalloc: fix high order __GFP_NOFAIL allocations"). > > With my limited understanding, I'm not sure why it can cause > deadlock here since it will fallback to order-0 allocation then, > and such allocation is just for short temporary uses again > because kmalloc doesn't support order > 1 short memory > allocation strictly. > deadlock on memory meands there is a memory leak causing system to be unable to allocate memory not actual *deadlock*. > Thanks, > Gao Xiang > -- Best Regards, Hailong.