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From: Kent Overstreet <kent.overstreet@gmail.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, Johannes Weiner <hannes@cmpxchg.org>,
Linus Torvalds <torvalds@linux-foundation.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 16:14:06 -0400 [thread overview]
Message-ID: <YVImDtfdgo+RXBe+@moria.home.lan> (raw)
In-Reply-To: <751358b2-aec2-43a3-cbbe-1f8c4469b6d3@suse.cz>
On Mon, Sep 27, 2021 at 09:07:21PM +0200, Vlastimil Babka wrote:
> On 9/27/2021 8:09 PM, Kent Overstreet wrote:
> > On Mon, Sep 27, 2021 at 07:05:26PM +0100, Matthew Wilcox wrote:
> >> On Mon, Sep 27, 2021 at 07:48:15PM +0200, Vlastimil Babka wrote:
> >>> Won't be easy to cram all that into two unsigned long's, or even a single
> >>> one. We should avoid storing anything in the free page itself. Allocating
> >>> some external structures to track free pages is going to have funny
> >>> bootstrap problems. Probably a major redesign would be needed...
> >>
> >> Wait, why do we want to avoid using the memory that we're allocating?
> >
> > The issue is where to stick the state for free pages. If that doesn't fit in two
> > ulongs, then we'd need a separate allocation, which means slab needs to be up
> > and running before free pages are initialized.
>
> So that's what I meant by the funny bootstrap problems - slab allocates pages
> from the buddy allocator. And well, not just bootstrap, imagine free memory
> becomes low, we need to reclaim pages, and in order to turn full pages to free
> buddy pages we need to allocate these slab structures, and the slab is full too
> and needs to allocate more backing pages...
>
> By "major redesign" I meant e.g. something along - bitmaps of free pages per
> each order? (instead of the free lists) Hm but I guess no, the worst case times
> searching for free pages would just suck...
We can have arrays of pointers to free pages - then within struct page we'd keep
the index of that page in the freelist array. To take a page off the middle of
the freelist we'd just swap it with the one at the end. And instead of using a
literal array, we'd want to use a simple radix tree.
next prev parent reply other threads:[~2021-09-27 20:14 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
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 [this message]
2021-09-28 11:21 ` David Laight
2021-09-27 18:33 ` Kirill A. Shutemov
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