From: ebiederm@xmission.com (Eric W. Biederman)
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>,
"Darrick J. Wong" <djwong@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [GIT PULL] Memory folios for v5.15
Date: Tue, 31 Aug 2021 13:50:35 -0500 [thread overview]
Message-ID: <87r1e95tz8.fsf@disp2133> (raw)
In-Reply-To: <YS0/GHBG15+2Mglk@cmpxchg.org> (Johannes Weiner's message of "Mon, 30 Aug 2021 16:27:04 -0400")
Johannes Weiner <hannes@cmpxchg.org> writes:
> On Mon, Aug 30, 2021 at 07:22:25PM +0100, Matthew Wilcox wrote:
>> On Mon, Aug 30, 2021 at 01:32:55PM -0400, Johannes Weiner wrote:
>> > > The mistake you're making is coupling "minimum mapping granularity" with
>> > > "minimum allocation granularity". We can happily build a system which
>> > > only allocates memory on 2MB boundaries and yet lets you map that memory
>> > > to userspace in 4kB granules.
>> >
>> > Yeah, but I want to do it without allocating 4k granule descriptors
>> > statically at boot time for the entirety of available memory.
>>
>> Even that is possible when bumping the PAGE_SIZE to 16kB. It needs a
>> bit of fiddling:
>>
>> static int insert_page_into_pte_locked(struct mm_struct *mm, pte_t *pte,
>> unsigned long addr, struct page *page, pgprot_t prot)
>> {
>> if (!pte_none(*pte))
>> return -EBUSY;
>> /* Ok, finally just insert the thing.. */
>> get_page(page);
>> inc_mm_counter_fast(mm, mm_counter_file(page));
>> page_add_file_rmap(page, false);
>> set_pte_at(mm, addr, pte, mk_pte(page, prot));
>> return 0;
>> }
>>
>> mk_pte() assumes that a struct page refers to a single pte. If we
>> revamped it to take (page, offset, prot), it could construct the
>> appropriate pte for the offset within that page.
>
> Right, page tables only need a pfn. The struct page is for us to
> maintain additional state about the object.
>
> For the objects that are subpage sized, we should be able to hold that
> state (shrinker lru linkage, referenced bit, dirtiness, ...) inside
> ad-hoc allocated descriptors.
>
> Descriptors which could well be what struct folio {} is today, IMO. As
> long as it doesn't innately assume, or will assume, in the API the
> 1:1+ mapping to struct page that is inherent to the compound page.
struct buffer_head any one?
I am being silly but when you say you want something that isn't a page
for caching that could be less than a page in size, it really sounds
like you want struct buffer_head.
The only actual problem I am aware of with struct buffer_head is that
it is a block device abstraction and does not map well to other
situations. Which makes network filesystems unable to use struct
buffer_head.
Eric
next prev parent reply other threads:[~2021-08-31 18:51 UTC|newest]
Thread overview: 162+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-23 19:01 [GIT PULL] Memory folios for v5.15 Matthew Wilcox
2021-08-23 21:26 ` Johannes Weiner
2021-08-23 22:06 ` Linus Torvalds
2021-08-24 2:20 ` Matthew Wilcox
2021-08-24 13:04 ` Matthew Wilcox
2021-08-23 22:15 ` Matthew Wilcox
2021-08-24 18:32 ` Johannes Weiner
2021-08-24 18:59 ` Linus Torvalds
2021-08-25 6:39 ` Christoph Hellwig
2021-08-24 19:44 ` Matthew Wilcox
2021-08-25 15:13 ` Johannes Weiner
2021-08-26 0:45 ` Darrick J. Wong
2021-08-27 14:07 ` Johannes Weiner
2021-08-27 18:44 ` Matthew Wilcox
2021-08-27 21:41 ` Dan Williams
2021-08-27 21:49 ` Matthew Wilcox
2021-08-30 17:32 ` Johannes Weiner
2021-08-30 18:22 ` Matthew Wilcox
2021-08-30 20:27 ` Johannes Weiner
2021-08-30 21:38 ` Matthew Wilcox
2021-08-31 17:40 ` Vlastimil Babka
2021-09-01 17:43 ` Johannes Weiner
2021-09-02 15:13 ` Zi Yan
2021-09-06 14:00 ` Vlastimil Babka
2021-08-31 18:50 ` Eric W. Biederman [this message]
2021-08-26 8:58 ` David Howells
2021-08-27 10:03 ` Johannes Weiner
2021-08-27 12:05 ` Matthew Wilcox
2021-08-27 10:49 ` David Howells
2021-08-24 15:54 ` David Howells
2021-08-24 17:56 ` Matthew Wilcox
2021-08-24 18:26 ` Linus Torvalds
2021-08-24 18:29 ` Linus Torvalds
2021-08-24 19:26 ` Theodore Ts'o
2021-08-24 19:34 ` David Howells
2021-08-24 20:02 ` Theodore Ts'o
2021-08-24 21:32 ` David Howells
2021-08-25 12:08 ` Jeff Layton
2021-08-24 19:01 ` Matthew Wilcox
2021-08-24 19:11 ` Linus Torvalds
2021-08-24 19:23 ` Matthew Wilcox
2021-08-24 19:44 ` Theodore Ts'o
2021-08-24 20:00 ` Matthew Wilcox
2021-08-25 6:32 ` Christoph Hellwig
2021-08-25 9:01 ` Rasmus Villemoes
2021-08-26 6:32 ` Amir Goldstein
2021-08-25 12:03 ` Jeff Layton
2021-08-26 0:59 ` Darrick J. Wong
2021-08-26 4:02 ` Nicholas Piggin
2021-09-01 12:58 ` Mike Rapoport
2021-08-24 19:35 ` David Howells
2021-08-24 20:35 ` Vlastimil Babka
2021-08-24 20:40 ` Vlastimil Babka
2021-08-24 19:11 ` David Howells
2021-08-24 19:25 ` Linus Torvalds
2021-08-24 19:38 ` Linus Torvalds
2021-08-24 19:48 ` Linus Torvalds
2021-08-26 17:18 ` Matthew Wilcox
2021-08-24 19:59 ` David Howells
2021-10-05 13:52 ` Matthew Wilcox
2021-10-05 17:29 ` Johannes Weiner
2021-10-05 17:32 ` David Hildenbrand
2021-10-05 18:30 ` Matthew Wilcox
2021-10-05 19:56 ` Jason Gunthorpe
2021-08-28 3:29 ` Matthew Wilcox
2021-09-09 12:43 ` Christoph Hellwig
2021-09-09 13:56 ` Vlastimil Babka
2021-09-09 18:16 ` Johannes Weiner
2021-09-09 18:44 ` Matthew Wilcox
2021-09-09 22:03 ` Johannes Weiner
2021-09-09 22:48 ` Matthew Wilcox
2021-09-09 19:17 ` John Hubbard
2021-09-09 19:23 ` Matthew Wilcox
2021-09-10 20:16 ` Folio discussion recap Kent Overstreet
2021-09-11 1:23 ` Kirill A. Shutemov
2021-09-13 11:32 ` Michal Hocko
2021-09-13 18:12 ` Johannes Weiner
2021-09-15 15:40 ` Johannes Weiner
2021-09-15 17:55 ` Damian Tometzki
2021-09-16 2:58 ` Darrick J. Wong
2021-09-16 16:54 ` Johannes Weiner
2021-09-17 5:24 ` Dave Chinner
2021-09-17 7:18 ` Christoph Hellwig
2021-09-17 16:31 ` Johannes Weiner
2021-09-17 20:57 ` Kirill A. Shutemov
2021-09-17 21:17 ` Kent Overstreet
2021-09-17 22:02 ` Kirill A. Shutemov
2021-09-17 22:21 ` Kent Overstreet
2021-09-17 23:15 ` Johannes Weiner
2021-09-20 10:03 ` Kirill A. Shutemov
2021-09-17 21:13 ` Kent Overstreet
2021-09-17 22:25 ` Theodore Ts'o
2021-09-17 23:35 ` Josef Bacik
2021-09-18 1:04 ` Dave Chinner
2021-09-18 4:51 ` Kent Overstreet
2021-09-20 1:04 ` Dave Chinner
2021-09-16 21:58 ` David Howells
2021-09-20 2:17 ` Matthew Wilcox
2021-09-21 19:47 ` Johannes Weiner
2021-09-21 20:38 ` Matthew Wilcox
2021-09-21 21:11 ` Kent Overstreet
2021-09-21 21:22 ` Folios for 5.15 request - Was: re: Folio discussion recap - Kent Overstreet
2021-09-22 15:08 ` Johannes Weiner
2021-09-22 15:46 ` Kent Overstreet
2021-09-22 16:26 ` Matthew Wilcox
2021-09-22 16:56 ` Chris Mason
2021-09-22 19:54 ` Matthew Wilcox
2021-09-22 20:15 ` Kent Overstreet
2021-09-22 20:21 ` Linus Torvalds
2021-09-23 5:42 ` Kent Overstreet
2021-09-23 18:00 ` Johannes Weiner
2021-09-23 19:31 ` Matthew Wilcox
2021-09-23 20:20 ` Kent Overstreet
2021-10-16 3:28 ` Matthew Wilcox
2021-10-18 16:47 ` Johannes Weiner
2021-10-18 18:12 ` Kent Overstreet
2021-10-18 20:45 ` Johannes Weiner
2021-10-19 16:11 ` Splitting struct page into multiple types " Kent Overstreet
2021-10-19 17:06 ` Gao Xiang
2021-10-19 17:34 ` Matthew Wilcox
2021-10-19 17:54 ` Gao Xiang
2021-10-20 17:46 ` Kent Overstreet
2021-10-19 17:37 ` Jason Gunthorpe
2021-10-19 21:14 ` David Howells
2021-10-18 18:28 ` Folios for 5.15 request " Matthew Wilcox
2021-10-18 21:56 ` Johannes Weiner
2021-10-18 23:16 ` Kirill A. Shutemov
2021-10-19 15:16 ` Johannes Weiner
2021-10-20 3:19 ` Matthew Wilcox
2021-10-20 7:50 ` David Hildenbrand
2021-10-20 17:26 ` Matthew Wilcox
2021-10-20 18:04 ` David Hildenbrand
2021-10-21 6:51 ` Christoph Hellwig
2021-10-21 7:21 ` David Hildenbrand
2021-10-21 12:03 ` Kent Overstreet
2021-10-21 12:35 ` David Hildenbrand
2021-10-21 12:38 ` Christoph Hellwig
2021-10-21 13:00 ` David Hildenbrand
2021-10-21 12:41 ` Matthew Wilcox
2021-10-20 17:39 ` Kent Overstreet
2021-10-21 21:37 ` Johannes Weiner
2021-10-22 1:52 ` Matthew Wilcox
2021-10-22 7:59 ` David Hildenbrand
2021-10-22 13:01 ` Matthew Wilcox
2021-10-22 14:40 ` David Hildenbrand
2021-10-23 2:22 ` Matthew Wilcox
2021-10-23 5:02 ` Christoph Hellwig
2021-10-23 9:58 ` David Hildenbrand
2021-10-23 16:00 ` Kent Overstreet
2021-10-23 21:41 ` Matthew Wilcox
2021-10-23 22:23 ` Kent Overstreet
2021-10-25 15:35 ` Johannes Weiner
2021-10-25 15:52 ` Matthew Wilcox
2021-10-25 16:05 ` Kent Overstreet
2021-10-16 19:07 ` Matthew Wilcox
2021-10-18 17:25 ` Johannes Weiner
2021-09-21 22:18 ` Folio discussion recap Matthew Wilcox
2021-09-23 0:45 ` Ira Weiny
2021-09-23 3:41 ` Matthew Wilcox
2021-09-23 22:12 ` Ira Weiny
2021-09-29 15:24 ` Matthew Wilcox
2021-09-21 21:59 ` Johannes Weiner
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