Message ID | 20220801184740.2134364-1-alexlzhu@fb.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | [v2] mm: fix alginment of VMA for memory mapped files on THP | expand |
On Mon, Aug 01, 2022 at 11:47:40AM -0700, alexlzhu@fb.com wrote: > From: alexlzhu <alexlzhu@fb.com> > > With CONFIG_READ_ONLY_THP_FOR_FS, the Linux kernel supports using THPs for > read-only mmapped files, such as shared libraries. However, the > kernel makes no attempt to actually align those mappings on 2MB boundaries, > which makes it impossible to use those THPs most of the time. This issue > applies to general file mapping THP as well as existing setups using > CONFIG_READ_ONLY_THP_FOR_FS. This is easily fixed by using > thp_get_unmapped_area for the unmapped_area function in btrfs, which is > what ext2, ext4, fuse, and xfs all use. Commit dbe6ec815641 ("ext2/4, xfs: call thp_get_unmapped_area() for pmd mappings") adds the callback for DAX, that btrfs does not support so it was left out. > The problem can be seen in > /proc/PID/smaps where THPeligible is set to 0 on mappings to eligible > shared object files as shown below. > > Before this patch: > > 7fc6a7e18000-7fc6a80cc000 r-xp 00000000 00:1e 199856 > /usr/lib64/libcrypto.so.1.1.1k > Size: 2768 kB > THPeligible: 0 > VmFlags: rd ex mr mw me > > With this patch the library is mapped at a 2MB aligned address: > > fbdfe200000-7fbdfe4b4000 r-xp 00000000 00:1e 199856 > /usr/lib64/libcrypto.so.1.1.1k > Size: 2768 kB > THPeligible: 1 > VmFlags: rd ex mr mw me > > This fixes the alignment of VMAs for any mmap of a file that has the > rd and ex permissions and size >= 2MB. The VMA alignment and > THPeligible field for anonymous memory is handled separately and > is thus not effected by this change. > > Signed-off-by: alexlzhu <alexlzhu@fb.com> Please use full name for signed-off. Also the subject should start with "btrfs:", this is not a memory management patch. Thanks.
> Commit dbe6ec815641 ("ext2/4, xfs: call thp_get_unmapped_area() for pmd > mappings") adds the callback for DAX, that btrfs does not support so it > was left out. Commit 1854bc6e2420 ("mm/readahead: Align file mappings for non-DAX”) removed the DAX requirement. We should now be able to call thp_get_unmapped_area() for btrfs. I’ll send out a v3 with the subject and sign off corrected. Thanks!
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 9dfde1af8a64..2423040db167 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -3808,6 +3808,7 @@ const struct file_operations btrfs_file_operations = { .mmap = btrfs_file_mmap, .open = btrfs_file_open, .release = btrfs_release_file, + .get_unmapped_area = thp_get_unmapped_area, .fsync = btrfs_sync_file, .fallocate = btrfs_fallocate, .unlocked_ioctl = btrfs_ioctl,