XArray: add xa_get_order
authorMatthew Wilcox (Oracle) <willy@infradead.org>
Fri, 16 Oct 2020 03:05:13 +0000 (20:05 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 16 Oct 2020 18:11:15 +0000 (11:11 -0700)
commit57417cebc96b57122a2207fc84a6077d20c84b4b
tree4a15c75bcc56f0c5392393a2d0672e4acc539a9e
parentf14312e1ed1e40dfed38bb70eb9a71d97a6b60f4
XArray: add xa_get_order

Patch series "Fix read-only THP for non-tmpfs filesystems".

As described more verbosely in the [3/3] changelog, we can inadvertently
put an order-0 page in the page cache which occupies 512 consecutive
entries.  Users are running into this if they enable the
READ_ONLY_THP_FOR_FS config option; see
https://bugzilla.kernel.org/show_bug.cgi?id=206569 and Qian Cai has also
reported it here:
https://lore.kernel.org/lkml/20200616013309.GB815@lca.pw/

This is a rather intrusive way of fixing the problem, but has the
advantage that I've actually been testing it with the THP patches, which
means that it sees far more use than it does upstream -- indeed, Song has
been entirely unable to reproduce it.  It also has the advantage that it
removes a few patches from my gargantuan backlog of THP patches.

This patch (of 3):

This function returns the order of the entry at the index.  We need this
because there isn't space in the shadow entry to encode its order.

[akpm@linux-foundation.org: export xa_get_order to modules]

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Qian Cai <cai@lca.pw>
Cc: Song Liu <songliubraving@fb.com>
Link: https://lkml.kernel.org/r/20200903183029.14930-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20200903183029.14930-2-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
include/linux/xarray.h
lib/test_xarray.c
lib/xarray.c