On Tue, Aug 02, 2022 at 01:32:46PM -0700, alexlzhu@xxxxxx wrote: > From: Alexander Zhu <alexlzhu@xxxxxx> > > 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. > > Initially btrfs had been left out in Commit 8c07fc452ac0 ("btrfs: fix > alginment of VMA for memory mapped files on THP") as btrfs does not support > DAX. However, 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. > > 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: Alexander Zhu <alexlzhu@xxxxxx> Added to misc-next, thanks.