From: Michal Hocko mhocko@suse.com
Commit c20cd45eb01748f0fba77a504f956b000df4ea73 upstream.
page_cache_read has been historically using page_cache_alloc_cold to allocate a new page. This means that mapping_gfp_mask is used as the base for the gfp_mask. Many filesystems are setting this mask to GFP_NOFS to prevent from fs recursion issues. page_cache_read is called from the vm_operations_struct::fault() context during the page fault. This context doesn't need the reclaim protection normally.
ceph and ocfs2 which call filemap_fault from their fault handlers seem to be OK because they are not taking any fs lock before invoking generic implementation. xfs which takes XFS_MMAPLOCK_SHARED is safe from the reclaim recursion POV because this lock serializes truncate and punch hole with the page faults and it doesn't get involved in the reclaim.
There is simply no reason to deliberately use a weaker allocation context when a __GFP_FS | __GFP_IO can be used. The GFP_NOFS protection might be even harmful. There is a push to fail GFP_NOFS allocations rather than loop within allocator indefinitely with a very limited reclaim ability. Once we start failing those requests the OOM killer might be triggered prematurely because the page cache allocation failure is propagated up the page fault path and end up in pagefault_out_of_memory.
We cannot play with mapping_gfp_mask directly because that would be racy wrt. parallel page faults and it might interfere with other users who really rely on NOFS semantic from the stored gfp_mask. The mask is also inode proper so it would even be a layering violation. What we can do instead is to push the gfp_mask into struct vm_fault and allow fs layer to overwrite it should the callback need to be called with a different allocation context.
Initialize the default to (mapping_gfp_mask | __GFP_FS | __GFP_IO) because this should be safe from the page fault path normally. Why do we care about mapping_gfp_mask at all then? Because this doesn't hold only reclaim protection flags but it also might contain zone and movability restrictions (GFP_DMA32, __GFP_MOVABLE and others) so we have to respect those.
Signed-off-by: Michal Hocko mhocko@suse.com Reported-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Acked-by: Jan Kara jack@suse.com Acked-by: Vlastimil Babka vbabka@suse.cz Cc: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Cc: Mel Gorman mgorman@suse.de Cc: Dave Chinner david@fromorbit.com Cc: Mark Fasheh mfasheh@suse.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Harsh Shandilya harsh@prjkt.io --- include/linux/mm.h | 4 ++++ mm/filemap.c | 8 ++++---- mm/memory.c | 17 +++++++++++++++++ 3 files changed, 25 insertions(+), 4 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h index 5adffb0a468f..9ac4697979e8 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -203,9 +203,13 @@ extern pgprot_t protection_map[16]; * * pgoff should be used in favour of virtual_address, if possible. If pgoff * is used, one may implement ->remap_pages to get nonlinear mapping support. + * + * MM layer fills up gfp_mask for page allocations but fault handler might + * alter it if its implementation requires a different allocation context. */ struct vm_fault { unsigned int flags; /* FAULT_FLAG_xxx flags */ + gfp_t gfp_mask; /* gfp mask to be used for allocations */ pgoff_t pgoff; /* Logical page offset based on vma */ void __user *virtual_address; /* Faulting virtual address */
diff --git a/mm/filemap.c b/mm/filemap.c index 7e6ab98d4d3c..aafeeefcb00d 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1746,18 +1746,18 @@ EXPORT_SYMBOL(generic_file_read_iter); * This adds the requested page to the page cache if it isn't already there, * and schedules an I/O to read in its contents from disk. */ -static int page_cache_read(struct file *file, pgoff_t offset) +static int page_cache_read(struct file *file, pgoff_t offset, gfp_t gfp_mask) { struct address_space *mapping = file->f_mapping; struct page *page; int ret;
do { - page = page_cache_alloc_cold(mapping); + page = __page_cache_alloc(gfp_mask|__GFP_COLD); if (!page) return -ENOMEM;
- ret = add_to_page_cache_lru(page, mapping, offset, GFP_KERNEL); + ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask & GFP_KERNEL); if (ret == 0) ret = mapping->a_ops->readpage(file, page); else if (ret == -EEXIST) @@ -1940,7 +1940,7 @@ no_cached_page: * We're only likely to ever get here if MADV_RANDOM is in * effect. */ - error = page_cache_read(file, offset); + error = page_cache_read(file, offset, vmf->gfp_mask);
/* * The page we want has now been added to the page cache. diff --git a/mm/memory.c b/mm/memory.c index 0c4f5e36b155..5a62c6a42143 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1973,6 +1973,20 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo copy_user_highpage(dst, src, va, vma); }
+static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma) +{ + struct file *vm_file = vma->vm_file; + + if (vm_file) + return mapping_gfp_mask(vm_file->f_mapping) | __GFP_FS | __GFP_IO; + + /* + * Special mappings (e.g. VDSO) do not have any file so fake + * a default GFP_KERNEL for them. + */ + return GFP_KERNEL; +} + /* * Notify the address space that the page is about to become writable so that * it can prohibit this or wait for the page to get into an appropriate state. @@ -1988,6 +2002,7 @@ static int do_page_mkwrite(struct vm_area_struct *vma, struct page *page, vmf.virtual_address = (void __user *)(address & PAGE_MASK); vmf.pgoff = page->index; vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE; + vmf.gfp_mask = __get_fault_gfp_mask(vma); vmf.page = page;
ret = vma->vm_ops->page_mkwrite(vma, &vmf); @@ -2670,6 +2685,7 @@ static int __do_fault(struct vm_area_struct *vma, unsigned long address, vmf.pgoff = pgoff; vmf.flags = flags; vmf.page = NULL; + vmf.gfp_mask = __get_fault_gfp_mask(vma);
ret = vma->vm_ops->fault(vma, &vmf); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) @@ -2834,6 +2850,7 @@ static void do_fault_around(struct vm_area_struct *vma, unsigned long address, vmf.pgoff = pgoff; vmf.max_pgoff = max_pgoff; vmf.flags = flags; + vmf.gfp_mask = __get_fault_gfp_mask(vma); vma->vm_ops->map_pages(vma, &vmf); }