lkml.org 
[lkml]   [2023]   [Apr]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH -V2] mm,unmap: avoid flushing TLB in batch if PTE is inaccessible
From

在 2023/4/24 下午2:54, Huang Ying 写道:
> Hi, Andrew,
>
> The version 1 of this patch was merged in mm-unstable branch. If you
> want to move that patch into mm-stable recently, it may be better to
> update that patch with this new version firstly. If you want to do
> that after v6.4-rc1, I will rebase this patch and resend it after
> v6.4-rc1 is released.
>
> Hi, Amit,
>
> The patch has been changed based on comments from Xin. I keep your
> "reviewed-by" because I think the change is trivial. But if you think
> it's inappropriate, I will change that.
>
> Best Regards,
> Huang, Ying
>
> ------------------------------->8------------------------------------------
> 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@intel.com
> Link: https://lore.kernel.org/oe-lkp/ab92aaddf1b52ede15e2c608696c36765a2602c1.camel@intel.com/
> Fixes: 7e12beb8ca2a ("migrate_pages: batch flushing TLB")
> Reported-by: kernel test robot <yujie.liu@intel.com>
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Reviewed-by: Nadav Amit <namit@vmware.com>
> Cc: haoxin <xhao@linux.alibaba.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: David Hildenbrand <david@redhat.com>
> ---
> mm/rmap.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 8632e02661ac..be19232e94f4 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -641,10 +641,14 @@ void try_to_unmap_flush_dirty(void)
> #define TLB_FLUSH_BATCH_PENDING_LARGE \
> (TLB_FLUSH_BATCH_PENDING_MASK / 2)
>
> -static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
> +static void set_tlb_ubc_flush_pending(struct mm_struct *mm, pte_t pteval)
> {
> struct tlbflush_unmap_batch *tlb_ubc = &current->tlb_ubc;
> int batch, nbatch;
> + bool writable = pte_dirty(pteval);
> +
> + if (!pte_accessible(mm, pteval))
> + return;

LGTM

Reviewed-by: Xin Hao <xhao@linux.alibaba.com>

>
> arch_tlbbatch_add_mm(&tlb_ubc->arch, mm);
> tlb_ubc->flush_required = true;
> @@ -731,7 +735,7 @@ void flush_tlb_batched_pending(struct mm_struct *mm)
> }
> }
> #else
> -static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
> +static void set_tlb_ubc_flush_pending(struct mm_struct *mm, pte_t pteval)
> {
> }
>
> @@ -1582,7 +1586,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
> */
> pteval = ptep_get_and_clear(mm, address, pvmw.pte);
>
> - set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
> + set_tlb_ubc_flush_pending(mm, pteval);
> } else {
> pteval = ptep_clear_flush(vma, address, pvmw.pte);
> }
> @@ -1963,7 +1967,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
> */
> pteval = ptep_get_and_clear(mm, address, pvmw.pte);
>
> - set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
> + set_tlb_ubc_flush_pending(mm, pteval);
> } else {
> pteval = ptep_clear_flush(vma, address, pvmw.pte);
> }

\
 
 \ /
  Last update: 2023-04-24 11:26    [W:0.037 / U:1.100 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site