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@xxxxxx/ 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. Matthew Wilcox (Oracle) (3): XArray: Add xa_get_order XArray: Add xas_split mm/filemap: Fix storing to a THP shadow entry Documentation/core-api/xarray.rst | 16 +-- include/linux/xarray.h | 22 ++++ lib/test_xarray.c | 62 ++++++++++ lib/xarray.c | 196 ++++++++++++++++++++++++++++-- mm/filemap.c | 42 +++++-- 5 files changed, 311 insertions(+), 27 deletions(-) -- 2.28.0
