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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: David Hildenbrand <david@redhat.com>,
	Matthew Wilcox <willy@infradead.org>,
	Kent Overstreet <kent.overstreet@gmail.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Darrick J. Wong" <djwong@kernel.org>,
	Christoph Hellwig <hch@infradead.org>,
	David Howells <dhowells@redhat.com>
Subject: Re: Struct page proposal
Date: Mon, 27 Sep 2021 12:04:57 -0700	[thread overview]
Message-ID: <CAHk-=whQE3eZdFgtoeRmXVsO93c-nSbdheTvtUJcztJaE_KKEw@mail.gmail.com> (raw)
In-Reply-To: <df6ad8ab-b3a9-6264-e699-28422a74f995@suse.cz>

On Mon, Sep 27, 2021 at 11:53 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> I was thinking of debug_pagealloc (unmaps free pages from direct map) but yeah,
> the list is longer.

In fact, the _original_ free page list was in the page itself, not in
'struct page'.

The original reason to move it into 'struct page' ended up being
performance, iirc.

Because of how now the free page list was always in the same cache
line set, the page allocator caused horrendous cache patterns on
direct-mapped caches.

Direct-mapped caches may thankfully be gone, and we have a lot of
other things that end up having that property of "same offset within a
page" just because of allocation patterns (task struct allocations
being but one example), but it might still be something to try to
avoid.

               Linus

  reply	other threads:[~2021-09-27 19:05 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-23  1:21 Struct page proposal Kent Overstreet
2021-09-23  3:23 ` Matthew Wilcox
2021-09-23  5:15   ` Kent Overstreet
2021-09-23 11:40     ` Mapcount of subpages Matthew Wilcox
2021-09-23 12:45       ` Kirill A. Shutemov
2021-09-23 21:10         ` Hugh Dickins
2021-09-23 21:54           ` Yang Shi
2021-09-23 22:23             ` Zi Yan
2021-09-23 23:48               ` Hugh Dickins
2021-09-24  0:25                 ` Zi Yan
2021-09-24  0:57                   ` Hugh Dickins
2021-09-24  1:11                 ` Yang Shi
2021-09-24  1:31                   ` Matthew Wilcox
2021-09-24  3:26                     ` Yang Shi
2021-09-24 23:05           ` Kirill A. Shutemov
2021-09-23 18:56       ` Mike Kravetz
2021-09-23  9:03 ` Struct page proposal David Hildenbrand
2021-09-23 15:22   ` Kent Overstreet
2021-09-23 15:34     ` David Hildenbrand
2021-09-27 17:48 ` Vlastimil Babka
2021-09-27 17:53   ` Kent Overstreet
2021-09-27 18:34     ` Linus Torvalds
2021-09-27 20:45       ` David Hildenbrand
2021-09-27 18:05   ` Matthew Wilcox
2021-09-27 18:09     ` Kent Overstreet
2021-09-27 18:12       ` Matthew Wilcox
2021-09-27 18:16         ` David Hildenbrand
2021-09-27 18:53           ` Vlastimil Babka
2021-09-27 19:04             ` Linus Torvalds [this message]
2021-09-27 18:16         ` Kent Overstreet
2021-09-28  3:19           ` Matthew Wilcox
2021-09-27 19:07       ` Vlastimil Babka
2021-09-27 20:14         ` Kent Overstreet
2021-09-28 11:21         ` David Laight
2021-09-27 18:33     ` Kirill A. Shutemov

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