Re: [RFC PATCH] mm: Stop filemap_read() from grabbing a superfluous page

[Kent Overstreet]

On Thu, Oct 07, 2021 at 01:01:48PM +0100, David Howells wrote:
> Under some circumstances, filemap_read() will allocate sufficient pages to
> read to the end of the file, call readahead/readpages on them and copy the
> data over - and then it will allocate another page at the EOF and call
> readpage on that and then ignore it.  This is unnecessary and a waste of
> time and resources.
> 
> filemap_read() *does* check for this, but only after it has already done
> the allocation and I/O.  Fix this by checking before calling
> filemap_get_pages() also.
> 
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> cc: linux-mm@xxxxxxxxx
> cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Link: https://lore.kernel.org/r/160588481358.3465195.16552616179674485179.stgit@xxxxxxxxxxxxxxxxxxxxxx/

Acked-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>