From: David Hildenbrand <david@redhat.com>
To: alexlzhu@fb.com, linux-mm@kvack.org
Cc: willy@infradead.org, hannes@cmpxchg.org,
akpm@linux-foundation.org, riel@surriel.com, kernel-team@fb.com,
linux-kernel@vger.kernel.org
Subject: Re: [RFC 2/3] mm: changes to split_huge_page() to free zero filled tail pages
Date: Fri, 26 Aug 2022 12:18:58 +0200 [thread overview]
Message-ID: <ead1bc0e-c9df-d590-3423-9cfa449167e7@redhat.com> (raw)
In-Reply-To: <490fcdd204ae129a2e43614a569a1cf4bdde9196.1661461643.git.alexlzhu@fb.com>
On 25.08.22 23:30, alexlzhu@fb.com wrote:
> From: Alexander Zhu <alexlzhu@fb.com>
>
> Currently, when /sys/kernel/mm/transparent_hugepage/enabled=always is set
> there are a large number of transparent hugepages that are almost entirely
> zero filled. This is mentioned in a number of previous patchsets
> including:
> https://lore.kernel.org/all/20210731063938.1391602-1-yuzhao@google.com/
> https://lore.kernel.org/all/
> 1635422215-99394-1-git-send-email-ningzhang@linux.alibaba.com/
>
> Currently, split_huge_page() does not have a way to identify zero filled
> pages within the THP. Thus these zero pages get remapped and continue to
> create memory waste. In this patch, we identify and free tail pages that
> are zero filled in split_huge_page(). In this way, we avoid mapping these
> pages back into page table entries and can free up unused memory within
> THPs. This is based off the previously mentioned patchset by Yu Zhao.
> However, we chose to free zero tail pages whenever they are encountered
> instead of only on reclaim or migration. We also add a self test to verify
> the RssAnon value to make sure zero pages are not remapped.
>
Isn't this to some degree splitting the THP (PMDs->PTEs + dissolve
compound page) and then letting KSM replace the zero-filled page by the
shared zeropage?
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2022-08-26 10:19 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-25 21:30 [RFC 0/3] THP Shrinker alexlzhu
2022-08-25 21:30 ` [RFC 1/3] mm: add thp_utilization metrics to debugfs alexlzhu
2022-08-27 0:11 ` Zi Yan
2022-08-29 20:19 ` Alex Zhu (Kernel)
2022-08-25 21:30 ` [RFC 2/3] mm: changes to split_huge_page() to free zero filled tail pages alexlzhu
2022-08-26 10:18 ` David Hildenbrand [this message]
2022-08-26 18:34 ` Alex Zhu (Kernel)
2022-08-26 21:18 ` Rik van Riel
2022-08-29 10:02 ` David Hildenbrand
2022-08-29 13:17 ` Rik van Riel
2022-08-30 12:33 ` David Hildenbrand
2022-08-30 21:54 ` Alex Zhu (Kernel)
2022-08-25 21:30 ` [RFC 3/3] mm: THP low utilization shrinker alexlzhu
2022-08-27 0:25 ` Zi Yan
2022-08-29 20:49 ` Alex Zhu (Kernel)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ead1bc0e-c9df-d590-3423-9cfa449167e7@redhat.com \
--to=david@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=alexlzhu@fb.com \
--cc=hannes@cmpxchg.org \
--cc=kernel-team@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=riel@surriel.com \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).