Re: [patch 2/3] vmscan: drop page_mapping_inuse()

[Rik van Riel <riel@redhat.com>]

On 02/22/2010 02:49 PM, Johannes Weiner wrote:
> page_mapping_inuse() is a historic predicate function for pages that
> are about to be reclaimed or deactivated.
>
> According to it, a page is in use when it is mapped into page tables
> OR part of swap cache OR backing an mmapped file.
>
> This function is used in combination with page_referenced(), which
> checks for young bits in ptes and the page descriptor itself for the
> PG_referenced bit.  Thus, checking for unmapped swap cache pages is
> meaningless as PG_referenced is not set for anonymous pages and
> unmapped pages do not have young ptes.  The test makes no difference.
>
> Protecting file pages that are not by themselves mapped but are part
> of a mapped file is also a historic leftover for short-lived things
> like the exec() code in libc.  However, the VM now does reference
> accounting and activation of pages at unmap time and thus the special
> treatment on reclaim is obsolete.
>
> This patch drops page_mapping_inuse() and switches the two callsites
> to use page_mapped() directly.
>
> Signed-off-by: Johannes Weiner<hannes@cmpxchg.org>

Reviewed-by: Rik van Riel <riel@redhat.com>