+ mm-migrate-simplify-the-refcount-validation-when-migrating-hugetlb-mapping.patch added to -mm tree

+ mm-migrate-simplify-the-refcount-validation-when-migrating-hugetlb-mapping.patch added to -mm tree

[Andrew Morton]

The patch titled
     Subject: mm: migrate: simplify the refcount validation when migrating hugetlb mapping
has been added to the -mm tree.  Its filename is
     mm-migrate-simplify-the-refcount-validation-when-migrating-hugetlb-mapping.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-migrate-simplify-the-refcount-validation-when-migrating-hugetlb-mapping.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-migrate-simplify-the-refcount-validation-when-migrating-hugetlb-mapping.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Baolin Wang <baolin.wang@linux.alibaba.com>
Subject: mm: migrate: simplify the refcount validation when migrating hugetlb mapping

There is no need to validate the hugetlb page's refcount before trying to
freeze the hugetlb page's expected refcount, instead we can just rely on
the page_ref_freeze() to simplify the validation.

Moreover we are always under the page lock when migrating the hugetlb page
mapping, which means nowhere else can remove it from the page cache, so we
can remove the xas_load() validation under the i_pages lock.

Link: https://lkml.kernel.org/r/eb2fbbeaef2b1714097b9dec457426d682ee0635.1649676424.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/mm/migrate.c~mm-migrate-simplify-the-refcount-validation-when-migrating-hugetlb-mapping
+++ a/mm/migrate.c
@@ -477,11 +477,6 @@ int migrate_huge_page_move_mapping(struc
 
 	xas_lock_irq(&xas);
 	expected_count = 2 + page_has_private(page);
-	if (page_count(page) != expected_count || xas_load(&xas) != page) {
-		xas_unlock_irq(&xas);
-		return -EAGAIN;
-	}
-
 	if (!page_ref_freeze(page, expected_count)) {
 		xas_unlock_irq(&xas);
 		return -EAGAIN;
_

Patches currently in -mm which might be from baolin.wang@linux.alibaba.com are

mm-migrate-simplify-the-refcount-validation-when-migrating-hugetlb-mapping.patch