mm/thp: remap_page() is only needed on anonymous THP

THP splitting's unmap_page() only sets TTU_SPLIT_FREEZE when PageAnon, and
migration entries are only inserted when TTU_MIGRATION (unused here) or
TTU_SPLIT_FREEZE is set: so it's just a waste of time for remap_page() to
search for migration entries to remove when !PageAnon.

Link: https://lkml.kernel.org/r/f987bc44-f28e-688d-2424-b4722153ed8@google.com
Fixes: baa355fd3314 ("thp: file pages support for split_huge_page()")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jue Wang <juew@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Wang Yugui <wangyugui@e16-tech.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index dc0a0c82a5acaa0694b9198f56eba9c33ca087aa..503c8e1aecc6bda55a64d45cddaaffb2b2b230eb 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2307,6 +2307,7 @@ static void unmap_page(struct page *page)
 
        VM_BUG_ON_PAGE(!PageHead(page), page);
 
+       /* If TTU_SPLIT_FREEZE is ever extended to file, update remap_page() */
        if (PageAnon(page))
                ttu_flags |= TTU_SPLIT_FREEZE;
 
@@ -2318,6 +2319,10 @@ static void unmap_page(struct page *page)
 static void remap_page(struct page *page, unsigned int nr)
 {
        int i;
+
+       /* If TTU_SPLIT_FREEZE is ever extended to file, remove this check */
+       if (!PageAnon(page))
+               return;
        if (PageTransHuge(page)) {
                remove_migration_ptes(page, page, true);
        } else {