Received-SPF: pass (google.com: domain of linux-kernel+bounces-199990-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Precedence: bulk
MIME-Version: 1.0
References: <20240604020549.1017540-1-yuanchu@google.com> <20240604020549.1017540-2-yuanchu@google.com>
In-Reply-To: <20240604020549.1017540-2-yuanchu@google.com>
From: Lance Yang <ioworker0@gmail.com>
Date: Tue, 4 Jun 2024 11:56:58 +0800
Message-ID: <CABzRoybRNbCQsz0PYUwEWWzUvR4FRcU3zp2Rzz9Fd4w3sK9hvQ@mail.gmail.com>
Subject: Re: [PATCH v2 1/8] mm: multi-gen LRU: ignore non-leaf pmd_young for force_scan=true
To: Yuanchu Xie <yuanchu@google.com>
Cc: David Hildenbrand <david@redhat.com>, "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>, 
	Khalid Aziz <khalid.aziz@oracle.com>, Henry Huang <henry.hj@antgroup.com>, 
	Yu Zhao <yuzhao@google.com>, Dan Williams <dan.j.williams@intel.com>, 
	Gregory Price <gregory.price@memverge.com>, Huang Ying <ying.huang@intel.com>, 
	Muhammad Usama Anjum <usama.anjum@collabora.com>, Kalesh Singh <kaleshsingh@google.com>, 
	Wei Xu <weixugc@google.com>, David Rientjes <rientjes@google.com>, 
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>, "Rafael J. Wysocki" <rafael@kernel.org>, 
	Andrew Morton <akpm@linux-foundation.org>, Johannes Weiner <hannes@cmpxchg.org>, 
	Michal Hocko <mhocko@kernel.org>, Roman Gushchin <roman.gushchin@linux.dev>, 
	Muchun Song <muchun.song@linux.dev>, Shuah Khan <shuah@kernel.org>, 
	Yosry Ahmed <yosryahmed@google.com>, Matthew Wilcox <willy@infradead.org>, 
	Sudarshan Rajagopalan <quic_sudaraja@quicinc.com>, Kairui Song <kasong@tencent.com>, 
	"Michael S. Tsirkin" <mst@redhat.com>, Vasily Averin <vasily.averin@linux.dev>, Nhat Pham <nphamcs@gmail.com>, 
	Miaohe Lin <linmiaohe@huawei.com>, Qi Zheng <zhengqi.arch@bytedance.com>, 
	Abel Wu <wuyun.abel@bytedance.com>, "Vishal Moola (Oracle)" <vishal.moola@gmail.com>, 
	Kefeng Wang <wangkefeng.wang@huawei.com>, linux-kernel@vger.kernel.org, 
	linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kselftest@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Hi Yuanchu,

Just a few nits below ;)

On Tue, Jun 4, 2024 at 10:06=E2=80=AFAM Yuanchu Xie <yuanchu@google.com> wr=
ote:
>
> When non-leaf pmd accessed bits are available, MGLRU page table walks
> can clear the non-leaf pmd accessed bit and ignore the accessed bit on
> the pte if it's on a different node, skipping a generation update as
> well. If another scan occurrs on the same node as said skipped pte.

s/occurrs/occurs

> the non-leaf pmd accessed bit might remain cleared and the pte accessed
> bits won't be checked. While this is sufficient for reclaim-driven
> aging, where the goal is to select a reasonably cold page, the access
> can be missed when aging proactively for workingset estimation of a of a

s/of a of a/of a

> node/memcg.
>
> In more detail, get_pfn_folio returns NULL if the folio's nid !=3D node
> under scanning, so the page table walk skips processing of said pte. Now
> the pmd_young flag on this pmd is cleared, and if none of the pte's are
> accessed before another scan occurrs on the folio's node, the pmd_young

s/occurrs/occurs

Thanks,
Lance

> check fails and the pte accessed bit is skipped.
>
> Since force_scan disables various other optimizations, we check
> force_scan to ignore the non-leaf pmd accessed bit.
>
> Signed-off-by: Yuanchu Xie <yuanchu@google.com>
> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index d55e8d07ffc4..73f3718b33f7 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3548,7 +3548,7 @@ static void walk_pmd_range(pud_t *pud, unsigned lon=
g start, unsigned long end,
>
>                 walk->mm_stats[MM_NONLEAF_TOTAL]++;
>
> -               if (should_clear_pmd_young()) {
> +               if (!walk->force_scan && should_clear_pmd_young()) {
>                         if (!pmd_young(val))
>                                 continue;
>
> --
> 2.45.1.467.gbab1589fc0-goog
>
>