From: Christoph Hellwig <hch@infradead.org>
To: Barry Song <21cnbao@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>,
akpm@linux-foundation.org, linux-mm@kvack.org, axboe@kernel.dk,
bala.seshasayee@linux.intel.com, chrisl@kernel.org,
david@redhat.com, hannes@cmpxchg.org,
kanchana.p.sridhar@intel.com, kasong@tencent.com,
nphamcs@gmail.com, ryan.roberts@arm.com,
senozhatsky@chromium.org, terrelln@fb.com,
usamaarif642@gmail.com, v-songbaohua@oppo.com,
wajdi.k.feghali@intel.com, willy@infradead.org,
ying.huang@linux.alibaba.com, yosryahmed@google.com,
baolin.wang@linux.alibaba.com
Subject: Re: [PATCH RFC] mm: map zero-filled pages to zero_pfn while doing swap-in
Date: Thu, 12 Dec 2024 00:50:30 -0800 [thread overview]
Message-ID: <Z1qj1gOdgEfevF5W@infradead.org> (raw)
In-Reply-To: <CAGsJ_4w9kvJcT2fw=cjLMwN_-+Q2pLaJ6qHhmh3MGvPNrGPxWQ@mail.gmail.com>
On Thu, Dec 12, 2024 at 09:46:03PM +1300, Barry Song wrote:
> On Thu, Dec 12, 2024 at 9:29 PM Christoph Hellwig <hch@infradead.org> wrote:
> >
> > On Thu, Dec 12, 2024 at 08:37:11PM +1300, Barry Song wrote:
> > > From: Barry Song <v-songbaohua@oppo.com>
> > >
> > > While developing the zeromap series, Usama observed that certain
> > > workloads may contain over 10% zero-filled pages. This may present
> > > an opportunity to save memory by mapping zero-filled pages to zero_pfn
> > > in do_swap_page(). If a write occurs later, do_wp_page() can
> > > allocate a new page using the Copy-on-Write mechanism.
> >
> > Shouldn't this be done during, or rather instead of swap out instead?
> > Swapping all zero pages out just to optimize the in-memory
> > representation on seems rather backwards.
>
> I’m having trouble understanding your point—it seems like you might
> not have fully read the code. :-)
I've not read the code at all, I've read your commit log.
> The situation is as follows: for a zero-filled page, we are currently
> allocating a new
> page unconditionally. By mapping this zero-filled page to zero_pfn, we could
> save the memory used by this page.
Yes. But why do that in swap-in and not swap-out?
next prev parent reply other threads:[~2024-12-12 8:50 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-12-12 7:37 Barry Song
2024-12-12 8:29 ` Christoph Hellwig
2024-12-12 8:46 ` Barry Song
2024-12-12 8:50 ` Christoph Hellwig [this message]
2024-12-12 8:54 ` Barry Song
2024-12-12 8:50 ` David Hildenbrand
2024-12-12 9:16 ` Barry Song
2024-12-12 16:25 ` Johannes Weiner
2024-12-13 1:47 ` Barry Song
2024-12-13 2:27 ` Barry Song
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