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    SubjectRe: [PATCH 5/6] vmscan: Do not writeback filesystem pages in direct reclaim
    Date

    again, very sorry for the delay.

    > When memory is under enough pressure, a process may enter direct
    > reclaim to free pages in the same manner kswapd does. If a dirty page is
    > encountered during the scan, this page is written to backing storage using
    > mapping->writepage. This can result in very deep call stacks, particularly
    > if the target storage or filesystem are complex. It has already been observed
    > on XFS that the stack overflows but the problem is not XFS-specific.
    >
    > This patch prevents direct reclaim writing back filesystem pages by checking
    > if current is kswapd or the page is anonymous before writing back. If the
    > dirty pages cannot be written back, they are placed back on the LRU lists
    > for either background writing by the BDI threads or kswapd. If in direct
    > lumpy reclaim and dirty pages are encountered, the process will stall for
    > the background flusher before trying to reclaim the pages again.
    >
    > As the call-chain for writing anonymous pages is not expected to be deep
    > and they are not cleaned by flusher threads, anonymous pages are still
    > written back in direct reclaim.
    >
    > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
    > Acked-by: Rik van Riel <riel@redhat.com>
    > Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
    > ---
    > mm/vmscan.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++------------
    > 1 files changed, 54 insertions(+), 15 deletions(-)
    >
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index d83812a..2d2b588 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c
    > @@ -139,6 +139,9 @@ static DECLARE_RWSEM(shrinker_rwsem);
    > #define scanning_global_lru(sc) (1)
    > #endif
    >
    > +/* Direct lumpy reclaim waits up to five seconds for background cleaning */
    > +#define MAX_SWAP_CLEAN_WAIT 50
    > +
    > static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
    > struct scan_control *sc)
    > {
    > @@ -645,11 +648,13 @@ static noinline_for_stack void free_page_list(struct list_head *free_pages)
    > */
    > static unsigned long shrink_page_list(struct list_head *page_list,
    > struct scan_control *sc,
    > - enum pageout_io sync_writeback)
    > + enum pageout_io sync_writeback,
    > + unsigned long *nr_still_dirty)
    > {
    > LIST_HEAD(ret_pages);
    > LIST_HEAD(free_pages);
    > int pgactivate = 0;
    > + unsigned long nr_dirty = 0;
    > unsigned long nr_reclaimed = 0;
    >
    > cond_resched();
    > @@ -743,6 +748,15 @@ static unsigned long shrink_page_list(struct list_head *page_list,
    > }
    >
    > if (PageDirty(page)) {
    > + /*
    > + * Only kswapd can writeback filesystem pages to
    > + * avoid risk of stack overflow
    > + */
    > + if (page_is_file_cache(page) && !current_is_kswapd()) {
    > + nr_dirty++;
    > + goto keep_locked;
    > + }
    > +
    > if (references == PAGEREF_RECLAIM_CLEAN)
    > goto keep_locked;
    > if (!may_enter_fs)
    > @@ -860,6 +874,8 @@ keep:
    > free_page_list(&free_pages);
    >
    > list_splice(&ret_pages, page_list);
    > +
    > + *nr_still_dirty = nr_dirty;
    > count_vm_events(PGACTIVATE, pgactivate);
    > return nr_reclaimed;
    > }
    > @@ -1242,12 +1258,14 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
    > struct scan_control *sc, int priority, int file)
    > {
    > LIST_HEAD(page_list);
    > + LIST_HEAD(putback_list);
    > unsigned long nr_scanned;
    > unsigned long nr_reclaimed = 0;
    > unsigned long nr_taken;
    > unsigned long nr_active;
    > unsigned long nr_anon;
    > unsigned long nr_file;
    > + unsigned long nr_dirty;
    >
    > while (unlikely(too_many_isolated(zone, file, sc))) {
    > congestion_wait(BLK_RW_ASYNC, HZ/10);
    > @@ -1296,28 +1314,49 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
    >
    > spin_unlock_irq(&zone->lru_lock);
    >
    > - nr_reclaimed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
    > + nr_reclaimed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC,
    > + &nr_dirty);
    >
    > /*
    > - * If we are direct reclaiming for contiguous pages and we do
    > + * If specific pages are needed such as with direct reclaiming
    > + * for contiguous pages or for memory containers and we do
    > * not reclaim everything in the list, try again and wait
    > - * for IO to complete. This will stall high-order allocations
    > - * but that should be acceptable to the caller
    > + * for IO to complete. This will stall callers that require
    > + * specific pages but it should be acceptable to the caller
    > */
    > - if (nr_reclaimed < nr_taken && !current_is_kswapd() &&
    > - sc->lumpy_reclaim_mode) {
    > - congestion_wait(BLK_RW_ASYNC, HZ/10);
    > + if (sc->may_writepage && !current_is_kswapd() &&
    > + (sc->lumpy_reclaim_mode || sc->mem_cgroup)) {
    > + int dirty_retry = MAX_SWAP_CLEAN_WAIT;
    >
    > - /*
    > - * The attempt at page out may have made some
    > - * of the pages active, mark them inactive again.
    > - */
    > - nr_active = clear_active_flags(&page_list, NULL);
    > - count_vm_events(PGDEACTIVATE, nr_active);
    > + while (nr_reclaimed < nr_taken && nr_dirty && dirty_retry--) {
    > + struct page *page, *tmp;
    > +
    > + /* Take off the clean pages marked for activation */
    > + list_for_each_entry_safe(page, tmp, &page_list, lru) {
    > + if (PageDirty(page) || PageWriteback(page))
    > + continue;
    > +
    > + list_del(&page->lru);
    > + list_add(&page->lru, &putback_list);
    > + }
    > +
    > + wakeup_flusher_threads(laptop_mode ? 0 : nr_dirty);

    ditto.
    wakeup_flusher_threads(0) is not correct?

    And, When flusher thread still don't start IO, this loop don't have proper
    waiting. do we need wait_on_page_dirty() or something?
    (similar wait_on_page_writeback)



    > + congestion_wait(BLK_RW_ASYNC, HZ/10);

    As we discussed, congestion_wait() don't works find if slow strage device
    is connected.


    >
    > - nr_reclaimed += shrink_page_list(&page_list, sc, PAGEOUT_IO_SYNC);
    > + /*
    > + * The attempt at page out may have made some
    > + * of the pages active, mark them inactive again.
    > + */
    > + nr_active = clear_active_flags(&page_list, NULL);
    > + count_vm_events(PGDEACTIVATE, nr_active);
    > +
    > + nr_reclaimed += shrink_page_list(&page_list, sc,
    > + PAGEOUT_IO_SYNC, &nr_dirty);

    After my patch, when PAGEOUT_IO_SYNC failure, retry is no good idea.
    can we remove this loop?


    > + }
    > }
    >
    > + list_splice(&putback_list, &page_list);
    > +
    > local_irq_disable();
    > if (current_is_kswapd())
    > __count_vm_events(KSWAPD_STEAL, nr_reclaimed);
    > --
    > 1.7.1
    >





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