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AJvYcCX5WRRd3s3Vw73bsD44B3/QfJSqV9TLK7xGk6kwQBUEva7iTC+Hx90Wed/uiPgybTSol26wUaVT46ORj7/5eCssXqo= X-Gm-Message-State: AOJu0YytcTYzdHUXJ0RGu5CVGZoPL41ykwraGkSCqzy3NjuPALc7wZZi ay0LwYD90wr5FdQMyKeRK3nH84IAqzHo14aHcLps0m3OInRAxwBSIL/ng2hsgvxdaVmGI5tZPY9 10YgMIH/YxLHBl+9CGal1E/YrUy8= X-Google-Smtp-Source: AGHT+IECkZ8whp4dApFE6haHXPl6o6J/n2sgKKnGRcec3Us/8UVBfSO1i0cA3VdpBEEwUrJ74+g0EWlnbSr9V9tRA1g= X-Received: by 2002:aa7:c502:0:b0:57c:677a:a941 with SMTP id 4fb4d7f45d1cf-587a0bfe1famr2478831a12.40.1719831011547; Mon, 01 Jul 2024 03:50:11 -0700 (PDT) MIME-Version: 1.0 References: <20240628130750.73097-1-ioworker0@gmail.com> <20240628130750.73097-3-ioworker0@gmail.com> <13dcf4be-8c5f-4697-adc1-b68c3da82d78@arm.com> In-Reply-To: <13dcf4be-8c5f-4697-adc1-b68c3da82d78@arm.com> From: Lance Yang Date: Mon, 1 Jul 2024 18:50:00 +0800 Message-ID: Subject: Re: [PATCH v2 2/2] mm: add docs for per-order mTHP split counters To: Ryan Roberts Cc: akpm@linux-foundation.org, dj456119@gmail.com, 21cnbao@gmail.com, david@redhat.com, shy828301@gmail.com, ziy@nvidia.com, libang.li@antgroup.com, baolin.wang@linux.alibaba.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mingzhe Yang Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 3738880019 X-Stat-Signature: zmmwxxu8cy1ty6gxxax4964a7y4iy5rx X-HE-Tag: 1719831012-640216 X-HE-Meta: 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 yyiMISj1 pX7zWtksmMpN9H+7KF3/XzEASHgNQV/1jkTG3sLaGGCnizKTH4EDf3LBLu2PgQx/prN+kTkv8VUty/vbD5e/j5CvNDVH8Gg0cHBm1NSLmvOeYjnZlz1vplVVvzKSxd7RM1nAvbCc2r6gDLCoWGNcBLYT6b1zvtWAcXxe9kFkRodxb17JfrGzcP61kI5dCM2Z4wWp8GbfkLzS2/X6hTRMbtW+cbUVqIQsEp8gzgZmuWRyNSLAv8C4PrZLVJQHSQq4xyU9Qbccf5DQN9ns3h2euJcOzBypOb8f4M+G5QAqqMNqqd5KcK7uexCpJFvlcFBsuf6fv/YewtS7C7HanolJO+LD5AZGhNSyk8UtXXc9AJRwzhWMnTKIBY+2IYen8HjXLi0hCN2XT1kZyM9Om9v5uc1k6nA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jul 1, 2024 at 4:31=E2=80=AFPM Ryan Roberts = wrote: > > On 28/06/2024 14:07, Lance Yang wrote: > > This commit introduces documentation for mTHP split counters in > > transhuge.rst. > > > > Signed-off-by: Mingzhe Yang > > Signed-off-by: Lance Yang > > --- > > Documentation/admin-guide/mm/transhuge.rst | 16 ++++++++++++++++ > > 1 file changed, 16 insertions(+) > > > > diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation= /admin-guide/mm/transhuge.rst > > index 1f72b00af5d3..709fe10b60f4 100644 > > --- a/Documentation/admin-guide/mm/transhuge.rst > > +++ b/Documentation/admin-guide/mm/transhuge.rst > > @@ -514,6 +514,22 @@ file_fallback_charge > > falls back to using small pages even though the allocation was > > successful. > > > I note at the top of this section there is a note: > > Monitoring usage > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > .. note:: > Currently the below counters only record events relating to > PMD-sized THP. Events relating to other THP sizes are not included. > > Which is out of date, now that we support mTHP stats. Perhaps it should b= e removed? Good catch! Let's remove that in this patch ;) > > > > > +split > > + is incremented every time a huge page is successfully split into > > + base pages. This can happen for a variety of reasons but a common > > + reason is that a huge page is old and is being reclaimed. > > + This action implies splitting any block mappings into PTEs. > > Now that I'm reading this, I'm reminded that Yang Shi suggested at LSFMM = that a > potential aid so solving the swap-out fragmentation problem is to split h= igh > orders to lower (but not 0) orders. I don't know if we would take that ro= ute, > but in principle it sounds like splitting mTHP to smaller mTHP might be > something we want some day. I wonder if we should spec this counter to al= so > include splits to smaller orders and not just splits to base pages? > > Actually looking at the code, I think split_huge_page_to_list_to_order(or= der>0) > would already increment this counter without actually splitting to base p= ages. > So the documantation should probably just reflect that. Yep, you're right. It=E2=80=99s important that the documentation reflects that to ensure consi= stency. How about "... is successfully split into smaller orders. This can..."? Thanks, Lance > > > + > > +split_failed > > + is incremented if kernel fails to split huge > > + page. This can happen if the page was pinned by somebody. > > + > > +split_deferred > > + is incremented when a huge page is put onto split > > + queue. This happens when a huge page is partially unmapped and > > + splitting it would free up some memory. Pages on split queue are > > + going to be split under memory pressure. > > + > > As the system ages, allocating huge pages may be expensive as the > > system uses memory compaction to copy data around memory to free a > > huge page for use. There are some counters in ``/proc/vmstat`` to help >