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

From: David Hildenbrand
Date: Wed May 31 2023 - 03:43:30 EST

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@xxxxxxxxxx>
cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
cc: David Hildenbrand <david@xxxxxxxxxx>
cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
cc: Jens Axboe <axboe@xxxxxxxxx>
cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
cc: Jan Kara <jack@xxxxxxx>
cc: Jeff Layton <jlayton@xxxxxxxxxx>
cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
cc: Hillf Danton <hdanton@xxxxxxxx>
cc: Christian Brauner <brauner@xxxxxxxxxx>
cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
cc: linux-fsdevel@xxxxxxxxxxxxxxx
cc: linux-block@xxxxxxxxxxxxxxx
cc: linux-kernel@xxxxxxxxxxxxxxx
cc: linux-mm@xxxxxxxxx

Acked-by: David Hildenbrand <david@xxxxxxxxxx>


David / dhildenb