[patch 092/192] mm/thp: remap_page() is only needed on anonymous THP

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From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx
Fixes: baa355fd3314 ("thp: file pages support for split_huge_page()")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jue Wang <juew@xxxxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Wang Yugui <wangyugui@xxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/huge_memory.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/mm/huge_memory.c~mm-thp-remap_page-is-only-needed-on-anonymous-thp
+++ a/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 {
_



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