From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>, Vlastimil Babka <vbabka@suse.cz>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Matthew Wilcox <willy@infradead.org>,
David Hildenbrand <david@redhat.com>,
Alistair Popple <apopple@nvidia.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Rik van Riel <riel@surriel.com>,
Suren Baghdasaryan <surenb@google.com>,
Yu Zhao <yuzhao@google.com>, Greg Thelen <gthelen@google.com>,
Shakeel Butt <shakeelb@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: [PATCH v2 12/13] mm/thp: collapse_file() do try_to_unmap(TTU_BATCH_FLUSH)
Date: Mon, 14 Feb 2022 18:40:55 -0800 (PST) [thread overview]
Message-ID: <c390e7b-7648-b3e9-9ae1-87c9b9e95ed4@google.com> (raw)
In-Reply-To: <55a49083-37f9-3766-1de9-9feea7428ac@google.com>
collapse_file() is using unmap_mapping_pages(1) on each small page found
mapped, unlike others (reclaim, migration, splitting, memory-failure) who
use try_to_unmap(). There are four advantages to try_to_unmap(): first,
its TTU_IGNORE_MLOCK option now avoids leaving mlocked page in pagevec;
second, its vma lookup uses i_mmap_lock_read() not i_mmap_lock_write();
third, it breaks out early if page is not mapped everywhere it might be;
fourth, its TTU_BATCH_FLUSH option can be used, as in page reclaim, to
save up all the TLB flushing until all of the pages have been unmapped.
Wild guess: perhaps it was originally written to use try_to_unmap(),
but hit the VM_BUG_ON_PAGE(page_mapped) after unmapping, because without
TTU_SYNC it may skip page table locks; but unmap_mapping_pages() never
skips them, so fixed the issue. I did once hit that VM_BUG_ON_PAGE()
since making this change: we could pass TTU_SYNC here, but I think just
delete the check - the race is very rare, this is an ordinary small page
so we don't need to be so paranoid about mapcount surprises, and the
page_ref_freeze() just below already handles the case adequately.
Signed-off-by: Hugh Dickins <hughd@google.com>
---
v2: same as v1.
mm/khugepaged.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index d5e387c58bde..e0883a33efd6 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1829,13 +1829,12 @@ static void collapse_file(struct mm_struct *mm,
}
if (page_mapped(page))
- unmap_mapping_pages(mapping, index, 1, false);
+ try_to_unmap(page, TTU_IGNORE_MLOCK | TTU_BATCH_FLUSH);
xas_lock_irq(&xas);
xas_set(&xas, index);
VM_BUG_ON_PAGE(page != xas_load(&xas), page);
- VM_BUG_ON_PAGE(page_mapped(page), page);
/*
* The page is expected to have page_count() == 3:
@@ -1899,6 +1898,13 @@ static void collapse_file(struct mm_struct *mm,
xas_unlock_irq(&xas);
xa_unlocked:
+ /*
+ * If collapse is successful, flush must be done now before copying.
+ * If collapse is unsuccessful, does flush actually need to be done?
+ * Do it anyway, to clear the state.
+ */
+ try_to_unmap_flush();
+
if (result == SCAN_SUCCEED) {
struct page *page, *tmp;
--
2.34.1
next prev parent reply other threads:[~2022-02-15 2:41 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-15 2:18 [PATCH v2 00/13] mm/munlock: rework of mlock+munlock page handling Hugh Dickins
2022-02-15 2:20 ` [PATCH v2 01/13] mm/munlock: delete page_mlock() and all its works Hugh Dickins
2022-02-15 2:21 ` [PATCH v2 02/13] mm/munlock: delete FOLL_MLOCK and FOLL_POPULATE Hugh Dickins
2022-02-15 2:23 ` [PATCH v2 03/13] mm/munlock: delete munlock_vma_pages_all(), allow oomreap Hugh Dickins
2022-02-15 2:26 ` [PATCH v2 04/13] mm/munlock: rmap call mlock_vma_page() munlock_vma_page() Hugh Dickins
2022-02-15 15:22 ` Matthew Wilcox
2022-02-15 21:38 ` Hugh Dickins
2022-02-15 23:21 ` Matthew Wilcox
2022-02-15 2:28 ` [PATCH v2 05/13] mm/munlock: replace clear_page_mlock() by final clearance Hugh Dickins
2022-02-15 2:29 ` [PATCH v2 06/13] mm/munlock: maintain page->mlock_count while unevictable Hugh Dickins
2022-02-15 2:31 ` [PATCH v2 07/13] mm/munlock: mlock_pte_range() when mlocking or munlocking Hugh Dickins
2022-02-18 6:35 ` [mm/munlock] 237b445401: stress-ng.remap.ops_per_sec -62.6% regression kernel test robot
2022-02-18 8:49 ` Hugh Dickins
2022-02-21 6:32 ` Hugh Dickins
2022-02-24 8:37 ` Oliver Sang
2022-02-15 2:33 ` [PATCH v2 08/13] mm/migrate: __unmap_and_move() push good newpage to LRU Hugh Dickins
2022-02-15 2:34 ` [PATCH v2 09/13] mm/munlock: delete smp_mb() from __pagevec_lru_add_fn() Hugh Dickins
2022-02-15 2:37 ` [PATCH v2 10/13] mm/munlock: mlock_page() munlock_page() batch by pagevec Hugh Dickins
2022-02-15 16:40 ` Matthew Wilcox
2022-02-15 21:02 ` Hugh Dickins
2022-02-15 22:56 ` Matthew Wilcox
2022-02-15 2:38 ` [PATCH v2 11/13] mm/munlock: page migration needs mlock pagevec drained Hugh Dickins
2022-02-15 2:40 ` Hugh Dickins [this message]
2022-02-15 2:42 ` [PATCH v2 13/13] mm/thp: shrink_page_list() avoid splitting VM_LOCKED THP Hugh Dickins
2022-02-15 19:35 ` [PATCH v2 00/13] mm/munlock: rework of mlock+munlock page handling Matthew Wilcox
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