The patch titled
Subject: mm,unmap: avoid flushing TLB in batch if PTE is inaccessible
has been added to the -mm mm-unstable branch. Its filename is
mmunmap-avoid-flushing-tlb-in-batch-if-pte-is-inaccessible.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mmunmap-avoid-flushing-tlb-in-batch-if-pte-is-inaccessible.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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 via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Huang Ying <ying.huang@xxxxxxxxx>
Subject: mm,unmap: avoid flushing TLB in batch if PTE is inaccessible
Date: Mon, 10 Apr 2023 15:52:24 +0800
0Day/LKP reported a performance regression for commit 7e12beb8ca2a
("migrate_pages: batch flushing TLB"). In the commit, the TLB flushing
during page migration is batched. So, in try_to_migrate_one(),
ptep_clear_flush() is replaced with set_tlb_ubc_flush_pending(). In
further investigation, it is found that the TLB flushing can be avoided in
ptep_clear_flush() if the PTE is inaccessible. In fact, we can optimize
in similar way for the batched TLB flushing too to improve the
performance.
So in this patch, we check pte_accessible() before
set_tlb_ubc_flush_pending() in try_to_unmap/migrate_one(). Tests show
that the benchmark score of the anon-cow-rand-mt test case of
vm-scalability test suite can improve up to 2.1% with the patch on a Intel
server machine. The TLB flushing IPI can reduce up to 44.3%.
Link: https://lore.kernel.org/oe-lkp/202303192325.ecbaf968-yujie.liu@xxxxxxxxx
Link: https://lore.kernel.org/oe-lkp/ab92aaddf1b52ede15e2c608696c36765a2602c1.camel@xxxxxxxxx/
Link: https://lkml.kernel.org/r/20230410075224.827740-1-ying.huang@xxxxxxxxx
Fixes: 7e12beb8ca2a ("migrate_pages: batch flushing TLB")
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Reported-by: kernel test robot <yujie.liu@xxxxxxxxx>
Reviewed-by: Nadav Amit <namit@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/rmap.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- a/mm/rmap.c~mmunmap-avoid-flushing-tlb-in-batch-if-pte-is-inaccessible
+++ a/mm/rmap.c
@@ -1580,7 +1580,8 @@ static bool try_to_unmap_one(struct foli
*/
pteval = ptep_get_and_clear(mm, address, pvmw.pte);
- set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
+ if (pte_accessible(mm, pteval))
+ set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
} else {
pteval = ptep_clear_flush(vma, address, pvmw.pte);
}
@@ -1961,7 +1962,8 @@ static bool try_to_migrate_one(struct fo
*/
pteval = ptep_get_and_clear(mm, address, pvmw.pte);
- set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
+ if (pte_accessible(mm, pteval))
+ set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
} else {
pteval = ptep_clear_flush(vma, address, pvmw.pte);
}
_
Patches currently in -mm which might be from ying.huang@xxxxxxxxx are
migrate_pages_batch-fix-statistics-for-longterm-pin-retry.patch
mmunmap-avoid-flushing-tlb-in-batch-if-pte-is-inaccessible.patch
