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

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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treatment on reclaim is obsolete.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@xxxxxxxxxxx>

Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>

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