On Mon, 2010-02-22 at 20:49 +0100, 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.
Nice catch!
>
> 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
I have been a question in the part.
You seem to solve my long question. :)
But I want to make sure it by any log.
Could you tell me where I find the discussion mail thread or git log at
that time?
Just out of curiosity.
> 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 treatment on reclaim is obsolete.
It does make sense.
>
> This patch drops page_mapping_inuse() and switches the two callsites
> to use page_mapped() directly.
>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
> mm/vmscan.c | 25 ++-----------------------
> 1 files changed, 2 insertions(+), 23 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c2db55b..a8e4cbe 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -262,27 +262,6 @@ unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
> return ret;
> }
>
> -/* Called without lock on whether page is mapped, so answer is unstable */
> -static inline int page_mapping_inuse(struct page *page)
> -{
> - struct address_space *mapping;
> -
> - /* Page is in somebody's page tables. */
> - if (page_mapped(page))
> - return 1;
> -
> - /* Be more reluctant to reclaim swapcache than pagecache */
> - if (PageSwapCache(page))
> - return 1;
> -
> - mapping = page_mapping(page);
> - if (!mapping)
> - return 0;
> -
> - /* File is mmap'd by somebody? */
> - return mapping_mapped(mapping);
> -}
> -
> static inline int is_page_cache_freeable(struct page *page)
> {
> /*
> @@ -603,7 +582,7 @@ static enum page_references page_check_references(struct page *page,
> if (vm_flags & VM_LOCKED)
> return PAGEREF_RECLAIM;
>
> - if (page_mapping_inuse(page))
> + if (page_mapped(page))
> return PAGEREF_ACTIVATE;
>
> /* Reclaim if clean, defer dirty pages to writeback */
> @@ -1378,7 +1357,7 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
> }
>
> /* page_referenced clears PageReferenced */
> - if (page_mapping_inuse(page) &&
> + if (page_mapped(page) &&
> page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
> nr_rotated++;
> /*
It's good to me.
But page_referenced already have been checked page_mapped.
How about folding alone page_mapped check into page_referenced's inner?
--
Kind regards,
Minchan Kim
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