On Thu 19-03-15 18:14:39, Dave Chinner wrote: > On Wed, Mar 18, 2015 at 03:55:28PM +0100, Michal Hocko wrote: > > On Wed 18-03-15 10:44:11, Rik van Riel wrote: > > > On 03/18/2015 10:09 AM, Michal Hocko wrote: > > > > 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, > > > > however, not called from the fs layer > > > > > > Is that true for filesystems that have directories in > > > the page cache? > > > > I haven't found any explicit callers of filemap_fault except for ocfs2 > > and ceph and those seem OK to me. Which filesystems you have in mind? > > Just about every major filesystem calls filemap_fault through the > .fault callout. That is right but the callback is called from the VM layer where we obviously do not take any fs locks (we are holding only mmap_sem for reading). Those who call filemap_fault directly (ocfs2 and ceph) and those who call the callback directly: qxl_ttm_fault, radeon_ttm_fault, kernfs_vma_fault, shm_fault seem to be safe from the reclaim recursion POV. radeon_ttm_fault takes a lock for reading but that one doesn't seem to be used from the reclaim context. Or did I miss your point? Are you concerned about some fs overloading filemap_fault and do some locking before delegating to filemap_fault? > C symbol: filemap_fault > > File Function Line > 0 9p/vfs_file.c <global> 831 .fault = filemap_fault, > 1 9p/vfs_file.c <global> 838 .fault = filemap_fault, > 2 btrfs/file.c <global> 2081 .fault = filemap_fault, > 3 cifs/file.c <global> 3242 .fault = filemap_fault, > 4 ext4/file.c <global> 215 .fault = filemap_fault, > 5 f2fs/file.c <global> 93 .fault = filemap_fault, > 6 fuse/file.c <global> 2062 .fault = filemap_fault, > 7 gfs2/file.c <global> 498 .fault = filemap_fault, > 8 nfs/file.c <global> 653 .fault = filemap_fault, > 9 nilfs2/file.c <global> 128 .fault = filemap_fault, > a ubifs/file.c <global> 1536 .fault = filemap_fault, > b xfs/xfs_file.c <global> 1420 .fault = filemap_fault, > > > > Btw. how would that work as we already have GFP_KERNEL allocation few > > lines below? > > GFP_KERNEL allocation for mappings is simply wrong. All mapping > allocations where the caller cannot pass a gfp_mask need to obey > the mapping_gfp_mask that is set by the mapping owner.... Hmm, I thought this is true only when the function might be called from the fs path. -- 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>