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Date: Thu, 5 Aug 2010 15:15:47 +0100
From: Mel Gorman <mel@....ul.ie>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, Dave Chinner <david@...morbit.com>,
Chris Mason <chris.mason@...cle.com>,
Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
Johannes Weiner <hannes@...xchg.org>,
Christoph Hellwig <hch@...radead.org>,
Wu Fengguang <fengguang.wu@...el.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 5/6] vmscan: Do not writeback filesystem pages in
direct reclaim
On Thu, Aug 05, 2010 at 03:59:37PM +0900, KOSAKI Motohiro wrote:
>
> again, very sorry for the delay.
>
No problem.
> > 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@....ul.ie>
> > Acked-by: Rik van Riel <riel@...hat.com>
> > Reviewed-by: Johannes Weiner <hannes@...xchg.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?
>
It's correct. When in lumpy mode, clean everything if the disk has to
spin up.
> 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)
>
If IO is not started on the correct pages, the flusher threads will be
rekicked for more work and another attempt is made at shrink_page_list.
>
>
> > + congestion_wait(BLK_RW_ASYNC, HZ/10);
>
> As we discussed, congestion_wait() don't works find if slow strage device
> is connected.
>
I currently support the removal of this congestion_wait(), but it belongs
in its own patch.
>
> >
> > - 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?
>
Such a removal belongs in the series related to lower latency of lumpy
reclaim. This patch is just about preventing dirty file pages being written
back by direct reclaim.
>
> > + }
> > }
> >
> > + list_splice(&putback_list, &page_list);
> > +
> > local_irq_disable();
> > if (current_is_kswapd())
> > __count_vm_events(KSWAPD_STEAL, nr_reclaimed);
> > --
> > 1.7.1
> >
>
>
>
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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