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SubjectRe: [rfc 2/3] mm: vmscan: treat inactive cycling as neutral
(11/2/2011 9:32 AM), Johannes Weiner wrote:
> Each page that is scanned but put back to the inactive list is counted
> as a successful reclaim, which tips the balance between file and anon
> lists more towards the cycling list.
>
> This does - in my opinion - not make too much sense, but at the same
> time it was not much of a problem, as the conditions that lead to an
> inactive list cycle were mostly temporary - locked page, concurrent
> page table changes, backing device congested - or at least limited to
> a single reclaimer that was not allowed to unmap or meddle with IO.
> More important than being moderately rare, those conditions should
> apply to both anon and mapped file pages equally and balance out in
> the end.
>
> Recently, we started cycling file pages in particular on the inactive
> list much more aggressively, for used-once detection of mapped pages,
> and when avoiding writeback from direct reclaim.
>
> Those rotated pages do not exactly speak for the reclaimability of the
> list they sit on and we risk putting immense pressure on file list for
> no good reason.
>
> Instead, count each page not reclaimed and put back to any list,
> active or inactive, as rotated, so they are neutral with respect to
> the scan/rotate ratio of the list class, as they should be.
>
> Signed-off-by: Johannes Weiner <jweiner@redhat.com>
> ---
> mm/vmscan.c | 9 ++++-----
> 1 files changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 39d3da3..6da66a7 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1360,7 +1360,9 @@ putback_lru_pages(struct zone *zone, struct scan_control *sc,
> */
> spin_lock(&zone->lru_lock);
> while (!list_empty(page_list)) {
> + int file;
> int lru;
> +
> page = lru_to_page(page_list);
> VM_BUG_ON(PageLRU(page));
> list_del(&page->lru);
> @@ -1373,11 +1375,8 @@ putback_lru_pages(struct zone *zone, struct scan_control *sc,
> SetPageLRU(page);
> lru = page_lru(page);
> add_page_to_lru_list(zone, page, lru);
> - if (is_active_lru(lru)) {
> - int file = is_file_lru(lru);
> - int numpages = hpage_nr_pages(page);
> - reclaim_stat->recent_rotated[file] += numpages;
> - }
> + file = is_file_lru(lru);
> + reclaim_stat->recent_rotated[file] += hpage_nr_pages(page);
> if (!pagevec_add(&pvec, page)) {
> spin_unlock_irq(&zone->lru_lock);
> __pagevec_release(&pvec);

When avoiding writeback from direct reclaim case, I think we shouldn't increase
recent_rotated because VM decided "the page should be eviceted, but also it
should be delayed". i'm not sure it's minor factor or not.




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