From: David Howells <dhowells@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: dhowells@redhat.com, Al Viro <viro@zeniv.linux.org.uk>,
Christoph Hellwig <hch@infradead.org>,
Matthew Wilcox <willy@infradead.org>,
Jens Axboe <axboe@kernel.dk>, Jan Kara <jack@suse.cz>,
Jeff Layton <jlayton@kernel.org>,
Logan Gunthorpe <logang@deltatee.com>,
linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
John Hubbard <jhubbard@nvidia.com>,
linux-mm@kvack.org
Subject: Re: [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator
Date: Mon, 23 Jan 2023 13:38:31 +0000 [thread overview]
Message-ID: <3911637.1674481111@warthog.procyon.org.uk> (raw)
In-Reply-To: <c742e47b-dcc0-1fef-dc8c-3bf85d26b046@redhat.com>
David Hildenbrand <david@redhat.com> wrote:
> That would be the ideal case: whenever intending to access page content, use
> FOLL_PIN instead of FOLL_GET.
>
> The issue that John was trying to sort out was that there are plenty of
> callsites that do a simple put_page() instead of calling
> unpin_user_page(). IIRC, handling that correctly in existing code -- what was
> pinned must be released via unpin_user_page() -- was the biggest workitem.
>
> Not sure how that relates to your work here (that's why I was asking): if you
> could avoid FOLL_GET, that would be great :)
Well, it simplifies things a bit.
I can make the new iov_iter_extract_pages() just do "pin" or "don't pin" and
do no ref-getting at all. Things can be converted over to "unpin the pages or
doing nothing" as they're converted over to using iov_iter_extract_pages()
from iov_iter_get_pages*().
The block bio code then only needs a single bit of state: pinned or not
pinned.
For cifs RDMA, do I need to make it pass in FOLL_LONGTERM? And does that need
a special cleanup?
sk_buff fragment handling could still be tricky. I'm thinking that in that
code I'll need to store FOLL_GET/PIN in the bottom two bits of the frag page
pointer. Sometimes it allocates a new page and attaches it (have ref);
sometimes it does zerocopy to/from a page (have pin) and sometimes it may be
pointing to a kernel buffer (don't pin or ref).
David
next prev parent reply other threads:[~2023-01-23 13:39 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-20 17:55 [PATCH v7 0/8] iov_iter: Improve page extraction (ref, pin or just list) David Howells
2023-01-20 17:55 ` [PATCH v7 1/8] iov_iter: Define flags to qualify page extraction David Howells
2023-01-21 13:01 ` Christoph Hellwig
2023-01-20 17:55 ` [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator David Howells
2023-01-21 13:01 ` Christoph Hellwig
2023-01-21 13:10 ` Christoph Hellwig
2023-01-21 13:30 ` David Howells
2023-01-21 13:33 ` Christoph Hellwig
2023-01-23 11:28 ` David Hildenbrand
2023-01-23 11:51 ` David Howells
2023-01-23 13:11 ` David Hildenbrand
2023-01-23 13:19 ` David Howells
2023-01-23 13:24 ` David Hildenbrand
2023-01-23 19:56 ` John Hubbard
2023-01-26 22:15 ` Al Viro
2023-01-26 23:41 ` David Hildenbrand
2023-01-27 0:05 ` David Howells
2023-01-27 0:20 ` David Hildenbrand
2023-01-23 13:38 ` David Howells [this message]
2023-01-23 14:20 ` David Hildenbrand
2023-01-23 14:48 ` Christoph Hellwig
2023-01-23 16:11 ` Jan Kara
2023-01-23 16:17 ` Christoph Hellwig
2023-01-23 23:07 ` John Hubbard
2023-01-24 5:57 ` Christoph Hellwig
2023-01-24 6:55 ` John Hubbard
2023-01-23 12:00 ` David Howells
2023-01-20 17:55 ` [PATCH v7 3/8] mm: Provide a helper to drop a pin/ref on a page David Howells
2023-01-20 17:55 ` [PATCH v7 4/8] block: Rename BIO_NO_PAGE_REF to BIO_PAGE_REFFED and invert the meaning David Howells
2023-01-21 13:04 ` Christoph Hellwig
2023-01-23 9:38 ` David Howells
2023-01-23 9:56 ` Christoph Hellwig
2023-01-20 17:55 ` [PATCH v7 5/8] block: Add BIO_PAGE_PINNED David Howells
2023-01-21 13:05 ` Christoph Hellwig
2023-01-20 17:55 ` [PATCH v7 6/8] block: Make bio structs pin pages rather than ref'ing if appropriate David Howells
2023-01-21 13:07 ` Christoph Hellwig
2023-01-23 11:28 ` David Howells
2023-01-23 14:49 ` Christoph Hellwig
2023-01-20 17:55 ` [PATCH v7 7/8] block: Fix bio_flagged() so that gcc can better optimise it David Howells
2023-01-20 17:55 ` [PATCH v7 8/8] mm: Renumber FOLL_GET and FOLL_PIN down David Howells
2023-01-20 18:59 ` Matthew Wilcox
2023-01-20 19:18 ` David Howells
2023-01-23 16:31 ` [PATCH v7 0/8] iov_iter: Improve page extraction (ref, pin or just list) Matthew Wilcox
2023-01-23 16:42 ` Jan Kara
2023-01-23 17:33 ` Matthew Wilcox
2023-01-23 22:53 ` John Hubbard
2023-01-24 10:29 ` Jan Kara
2023-01-24 13:21 ` Christoph Hellwig
2023-01-23 16:38 ` David Howells
2023-01-23 16:42 ` Matthew Wilcox
2023-01-23 17:25 ` Jan Kara
2023-01-24 10:24 ` David Hildenbrand
2023-01-23 17:19 ` David Howells
2023-01-23 18:04 ` Matthew Wilcox
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