linux-kernel - Re: [PATCH v4 2/3] mm: Provide a function to get an additional pin on a page

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Date:   Wed, 31 May 2023 09:42:26 +0200
From:   David Hildenbrand <david@...hat.com>
To:     David Howells <dhowells@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Lorenzo Stoakes <lstoakes@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Hillf Danton <hdanton@...a.com>,
        Christian Brauner <brauner@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH v4 2/3] mm: Provide a function to get an additional pin on
 a page

On 26.05.23 23:41, David Howells wrote:
> Provide a function to get an additional pin on a page that we already have
> a pin on.  This will be used in fs/direct-io.c when dispatching multiple
> bios to a page we've extracted from a user-backed iter rather than redoing
> the extraction.
> 

I guess this function is only used for "replicating" an existing pin, 
and not changing the semantics of an existing pin: something that was 
pinned !FOLL_LONGTERM cannot suddenly become effectively pinned 
FOLL_LONGTERM.

Out of curiosity, could we end up passing in an anonymous page, or is 
this almost exclusively for pagecache+zero pages? (I rememebr John H. 
had a similar patch where he said it would not apply to anon pages)

> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Christoph Hellwig <hch@...radead.org>
> cc: David Hildenbrand <david@...hat.com>
> cc: Lorenzo Stoakes <lstoakes@...il.com>
> cc: Andrew Morton <akpm@...ux-foundation.org>
> cc: Jens Axboe <axboe@...nel.dk>
> cc: Al Viro <viro@...iv.linux.org.uk>
> cc: Matthew Wilcox <willy@...radead.org>
> cc: Jan Kara <jack@...e.cz>
> cc: Jeff Layton <jlayton@...nel.org>
> cc: Jason Gunthorpe <jgg@...dia.com>
> cc: Logan Gunthorpe <logang@...tatee.com>
> cc: Hillf Danton <hdanton@...a.com>
> cc: Christian Brauner <brauner@...nel.org>
> cc: Linus Torvalds <torvalds@...ux-foundation.org>
> cc: linux-fsdevel@...r.kernel.org
> cc: linux-block@...r.kernel.org
> cc: linux-kernel@...r.kernel.org
> cc: linux-mm@...ck.org
> ---

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb