On Thu, Mar 19, 2015 at 01:44:41PM +0100, Michal Hocko wrote: > 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? The latter: https://git.kernel.org/cgit/linux/kernel/git/dgc/linux-xfs.git/commit/?h=xfs-mmap-lock&id=de0e8c20ba3a65b0f15040aabbefdc1999876e6b > > 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. How do you know in, say, mpage_readpages, you aren't being called from a fs path that holds locks? e.g. we can get there from ext4 doing readdir, so it is holding an i_mutex lock at that point. Many other paths into mpages_readpages don't hold locks, but there are some that do, and those that do need functionals like this to obey the mapping_gfp_mask because it is set appropriately for the allocation context of the inode that owns the mapping.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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>