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