On Thu, 28 Apr 2022, Greg Kroah-Hartman wrote: > From: Hugh Dickins <hughd@xxxxxxxxxx> > > commit bd55b0c2d64e84a75575f548a33a3dfecc135b65 upstream. > > PageDoubleMap is maintained differently for anon and for shmem+file: the > shmem+file one was never cleared, because a safe place to do so could > not be found; so it would blight future use of the cached hugepage until > evicted. > > See https://lore.kernel.org/lkml/1571938066-29031-1-git-send-email-yang.shi@xxxxxxxxxxxxxxxxx/ > > But page_add_file_rmap() does provide a safe place to do so (though later > than one might wish): allowing testing to return to an initial state > without a damaging drop_caches. > > Link: https://lkml.kernel.org/r/61c5cf99-a962-9a25-597a-53ab1bd8fbc0@xxxxxxxxxx > Fixes: 9a73f61bdb8a ("thp, mlock: do not mlock PTE-mapped file huge pages") > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> > Reviewed-by: Yang Shi <shy828301@xxxxxxxxx> > Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> NAK. I thought we had a long-standing agreement that AUTOSEL does not try to add patches from akpm's tree which had not been marked for stable. (Whereas, if a developer asks for such a patch to be added to stable later, and verifies the result, that's of course a different matter.) I've chosen to answer to this patch of my 3 in your 14 AUTOSELs, because this one is just an improvement, not at all a bugfix needed for stable (maybe AUTOSEL noticed "racy" or "safely" in the comments, and misunderstood). The "Fixes" was intended to help any humans who wanted to backport into their trees. I do recall that this 13/14, and 14/14, are mods to mm/rmap.c which followed other (mm/munlock) mods to mm/rmap.c in 5.18-rc1, which affected the out path of the function involved, and somehow made 14/14 a little cleaner. I'm sorry, but I just don't rate it worth my time at the moment, to verify whether 14/14 happens to have ended up as a correct patch or not. And nobody can verify them without these AUTOSELs saying to which tree they are targeted - 5.17 I suppose. Hugh > --- > mm/rmap.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/mm/rmap.c b/mm/rmap.c > index 9e27f9f038d3..444d0d958aff 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1252,6 +1252,17 @@ void page_add_file_rmap(struct page *page, bool compound) > } > if (!atomic_inc_and_test(compound_mapcount_ptr(page))) > goto out; > + > + /* > + * It is racy to ClearPageDoubleMap in page_remove_file_rmap(); > + * but page lock is held by all page_add_file_rmap() compound > + * callers, and SetPageDoubleMap below warns if !PageLocked: > + * so here is a place that DoubleMap can be safely cleared. > + */ > + VM_WARN_ON_ONCE(!PageLocked(page)); > + if (nr == nr_pages && PageDoubleMap(page)) > + ClearPageDoubleMap(page); > + > if (PageSwapBacked(page)) > __mod_lruvec_page_state(page, NR_SHMEM_PMDMAPPED, > nr_pages); > -- > 2.36.0
