From: Andrew Morton <akpm@linux-foundation.org>
To: Peter Xu <peterx@redhat.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>,
aarcange@redhat.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, 21cnbao@gmail.com,
ngeoffray@google.com, Suren Baghdasaryan <surenb@google.com>,
Kalesh Singh <kaleshsingh@google.com>,
Barry Song <v-songbaohua@oppo.com>,
David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH v3] userfaultfd: opportunistic TLB-flush batching for present pages in MOVE
Date: Thu, 7 Aug 2025 15:54:01 -0700 [thread overview]
Message-ID: <20250807155401.683c77b0d0cb5c9ec88089e6@linux-foundation.org> (raw)
In-Reply-To: <aJT7qQzEs_p36yfI@x1.local>
On Thu, 7 Aug 2025 15:16:57 -0400 Peter Xu <peterx@redhat.com> wrote:
> Hi, Lokesh,
>
> On Thu, Aug 07, 2025 at 03:39:02AM -0700, Lokesh Gidra wrote:
> > MOVE ioctl's runtime is dominated by TLB-flush cost, which is required
> > for moving present pages. Mitigate this cost by opportunistically
> > batching present contiguous pages for TLB flushing.
> >
> > Without batching, in our testing on an arm64 Android device with UFFD GC,
> > which uses MOVE ioctl for compaction, we observed that out of the total
> > time spent in move_pages_pte(), over 40% is in ptep_clear_flush(), and
> > ~20% in vm_normal_folio().
> >
> > With batching, the proportion of vm_normal_folio() increases to over
> > 70% of move_pages_pte() without any changes to vm_normal_folio().
>
> Do you know why vm_normal_folio() could be expensive? I still see quite
> some other things this path needs to do.
Maybe as explained here?
https://lkml.kernel.org/r/20250807185819.199865-1-lorenzo.stoakes@oracle.com
next prev parent reply other threads:[~2025-08-07 22:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-07 10:39 Lokesh Gidra
2025-08-07 19:16 ` Peter Xu
2025-08-07 22:54 ` Andrew Morton [this message]
2025-08-08 16:41 ` Lokesh Gidra
2025-08-08 16:29 ` Lokesh Gidra
2025-08-10 6:31 ` Lokesh Gidra
2025-08-11 14:00 ` Peter Xu
2025-08-12 14:01 ` Lokesh Gidra
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