lkml.org 
[lkml]   [2016]   [Jul]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 5/5] mm, vmscan: Account for skipped pages as a partial scan
    On Thu, Jul 21, 2016 at 03:11:01PM +0100, Mel Gorman wrote:
    > Page reclaim determines whether a pgdat is unreclaimable by examining how
    > many pages have been scanned since a page was freed and comparing that to
    > the LRU sizes. Skipped pages are not reclaim candidates but contribute to
    > scanned. This can prematurely mark a pgdat as unreclaimable and trigger
    > an OOM kill.
    >
    > This patch accounts for skipped pages as a partial scan so that an
    > unreclaimable pgdat will still be marked as such but by scaling the cost
    > of a skip, it'll avoid the pgdat being marked prematurely.
    >
    > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
    > ---
    > mm/vmscan.c | 20 ++++++++++++++++++--
    > 1 file changed, 18 insertions(+), 2 deletions(-)
    >
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index 6810d81f60c7..e5af357dd4ac 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c
    > @@ -1424,7 +1424,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
    > LIST_HEAD(pages_skipped);
    >
    > for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
    > - !list_empty(src); scan++) {
    > + !list_empty(src);) {
    > struct page *page;
    >
    > page = lru_to_page(src);
    > @@ -1438,6 +1438,12 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
    > continue;
    > }
    >
    > + /*
    > + * Account for scanned and skipped separetly to avoid the pgdat
    > + * being prematurely marked unreclaimable by pgdat_reclaimable.
    > + */
    > + scan++;
    > +
    > switch (__isolate_lru_page(page, mode)) {
    > case 0:
    > nr_pages = hpage_nr_pages(page);
    > @@ -1465,14 +1471,24 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
    > */
    > if (!list_empty(&pages_skipped)) {
    > int zid;
    > + unsigned long total_skipped = 0;
    >
    > - list_splice(&pages_skipped, src);
    > for (zid = 0; zid < MAX_NR_ZONES; zid++) {
    > if (!nr_skipped[zid])
    > continue;
    >
    > __count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
    > + total_skipped += nr_skipped[zid];
    > }
    > +
    > + /*
    > + * Account skipped pages as a partial scan as the pgdat may be
    > + * close to unreclaimable. If the LRU list is empty, account
    > + * skipped pages as a full scan.
    > + */

    node-lru made OOM detection lengthy because a freeing of any zone will
    reset NR_PAGES_SCANNED easily so that it's hard to meet a situation
    pgdat_reclaimable returns *false*.

    When I perform stress test, it seems I encounter the situation easily
    although I have no number now.

    Anyway, this patch makes sense to me because it's better than now.
    About accounting scan, I supports this idea.

    But still, I doubt it's okay to continue skipping pages under
    irq-disabled-spin lock without any condition.

    \
     
     \ /
      Last update: 2016-07-25 11:21    [W:3.893 / U:0.296 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site