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Mon, 16 Feb 2026 07:55:43 -0800 (PST) MIME-Version: 1.0 References: <20260214084514.2842745-1-haowenchao22@gmail.com> In-Reply-To: From: Wenchao Hao Date: Mon, 16 Feb 2026 23:55:31 +0800 X-Gm-Features: AaiRm51KD8ke76MeCQCtufCwLmalDJ2FNTUwXvE7u9dyzD1mLpvwzn203IhKnEc Message-ID: Subject: Re: [PATCH] mm: Add AnonZero accounting for zero-filled anonymous pages To: Matthew Wilcox Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 28F2240003 X-Stat-Signature: q6ygzqte88kq9twxun34rs5yg4xc1dr5 X-Rspam-User: X-HE-Tag: 1771257343-754983 X-HE-Meta: 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 CSqMdb6J fjz+3yKEKduVbMFKugexB90lC3oFx5D3tjm23xfJf+rFHATAtL8beoQeLcQ== 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, Feb 16, 2026 at 10:23=E2=80=AFPM Matthew Wilcox wrote: > > On Sat, Feb 14, 2026 at 04:45:14PM +0800, Wenchao Hao wrote: > > Add kernel command line option "count_zero_page" to track anonymous pag= es > > have been allocated and mapped to userspace but zero-filled. > > > > This feature is mainly used to debug large folio mechanism, which > > pre-allocates and map more pages than actually needed, leading to memor= y > > waste from unaccessed pages. > > Why are you trying to get this upstream when you admitted in an earlier > email this is just for your internal use? > I see this as a debugging feature, not limited to internal use only. Our real goal is to gain more precise visibility into how system memory is = used. A basic requirement is to measure the memory overhead caused by anonymous hugepages that have been pre-allocated but never accessed. With this information, we can implement various policies: - Allocate only 4K pages for applications that suffer severe memory waste = from anonymous hugepages. - Evaluate per-process hugepage waste during low system load and proactivel= y split hugepages accordingly. So I believe this debugging feature still provides value when merged upstre= am. Currently, there is no effective way to account for memory waste from pre-allocated but unused anonymous hugepages, and this feature fills that gap. Or do you = have any suggestions about how to get this info? > Why do you think that "unaccessed pages" are the only, or even the > largest source of extra memory consumption? The vast majority of files > are never mmaped. > In my view, memory waste from anonymous hugepages is less acceptable than t= hat from file pages. Although file pages may also be unmapped, a cache hit can still reduce I/O overhead. By contrast, pre-allocated anonymous hugepages that are never accessed repr= esent pure waste. Furthermore, the total number of unmapped file pages can already be estimated from /proc/meminfo, so we can already apply policies to control file page waste. >From my research, many memory-sensitive environments already apply special policies for file pages=E2=80=94for example, the RFC patch from vivo that manages readahead file pages separately: https://lore.kernel.org/linux-mm/20250916072226.220426-1-liulei.rjpt@vivo.c= om/ But file page waste is not the main point I want to focus on here. Thanks.