+ mm-improve-the-comment-in-isolate_migratepages_block.patch added to mm-unstable branch

+ mm-improve-the-comment-in-isolate_migratepages_block.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: improve the comment in isolate_migratepages_block()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-improve-the-comment-in-isolate_migratepages_block.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-improve-the-comment-in-isolate_migratepages_block.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Matthew Wilcox <willy@infradead.org>
Subject: mm: improve the comment in isolate_migratepages_block()
Date: Thu, 27 Jul 2023 21:39:44 +0100

A recent patch shows that not everybody understands that "stabilise the
mapping" really means "prevent the mapping from being freed", so change
the wording to hopefully make that more clear.

Link: https://lkml.kernel.org/r/ZMLWEB4m3zvX6SBN@casper.infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/compaction.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

--- a/mm/compaction.c~mm-improve-the-comment-in-isolate_migratepages_block
+++ a/mm/compaction.c
@@ -1095,13 +1095,13 @@ isolate_migratepages_block(struct compac
 			bool migrate_dirty;
 
 			/*
-			 * Only pages without mappings or that have a
-			 * ->migrate_folio callback are possible to migrate
-			 * without blocking. However, we can be racing with
-			 * truncation so it's necessary to lock the page
-			 * to stabilise the mapping as truncation holds
-			 * the page lock until after the page is removed
-			 * from the page cache.
+			 * Only folios without mappings or that have
+			 * a ->migrate_folio callback are possible to
+			 * migrate without blocking.  However, we may
+			 * be racing with truncation, which can free
+			 * the mapping.  Truncation holds the folio lock
+			 * until after the folio is removed from the page
+			 * cache so holding it ourselves is sufficient.
 			 */
 			if (!folio_trylock(folio))
 				goto isolate_fail_put;
_

Patches currently in -mm which might be from willy@infradead.org are

mm-drop-per-vma-lock-when-returning-vm_fault_retry-or-vm_fault_completed-fix.patch
rmap-pass-the-folio-to-__page_check_anon_rmap.patch
highmem-add-memcpy_to_folio-and-memcpy_from_folio.patch
affs-convert-affs_symlink_read_folio-to-use-the-folio.patch
affs-convert-data-read-and-write-to-use-folios.patch
migrate-use-folio_set_bh-instead-of-set_bh_page.patch
ntfs3-convert-ntfs_get_block_vbo-to-use-a-folio.patch
jbd2-use-a-folio-in-jbd2_journal_write_metadata_buffer.patch
buffer-remove-set_bh_page.patch
zswap-make-zswap_store-take-a-folio.patch
memcg-convert-get_obj_cgroup_from_page-to-get_obj_cgroup_from_folio.patch
swap-remove-some-calls-to-compound_head-in-swap_readpage.patch
zswap-make-zswap_load-take-a-folio.patch
mm-remove-config_per_vma_lock-ifdefs.patch
mm-allow-per-vma-locks-on-file-backed-vmas.patch
mm-move-fault_flag_vma_lock-check-from-handle_mm_fault.patch
mm-handle-pud-faults-under-the-vma-lock.patch
mm-handle-some-pmd-faults-under-the-vma-lock.patch
mm-move-fault_flag_vma_lock-check-down-in-handle_pte_fault.patch
mm-move-fault_flag_vma_lock-check-down-from-do_fault.patch
mm-run-the-fault-around-code-under-the-vma-lock.patch
mm-handle-swap-and-numa-pte-faults-under-the-vma-lock.patch
mm-handle-faults-that-merely-update-the-accessed-bit-under-the-vma-lock.patch
mm-handle-faults-that-merely-update-the-accessed-bit-under-the-vma-lock-fix.patch
mm-improve-the-comment-in-isolate_migratepages_block.patch