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Message-Id: <20100805153257.31D2.A69D9226@jp.fujitsu.com>
Date: Thu, 5 Aug 2010 15:45:24 +0900 (JST)
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To: Mel Gorman <mel@....ul.ie>
Cc: kosaki.motohiro@...fujitsu.com,
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 6/6] vmscan: Kick flusher threads to clean pages when reclaim is encountering dirty pages
sorry for the _very_ delayed review.
> There are a number of cases where pages get cleaned but two of concern
> to this patch are;
> o When dirtying pages, processes may be throttled to clean pages if
> dirty_ratio is not met.
> o Pages belonging to inodes dirtied longer than
> dirty_writeback_centisecs get cleaned.
>
> The problem for reclaim is that dirty pages can reach the end of the LRU if
> pages are being dirtied slowly so that neither the throttling or a flusher
> thread waking periodically cleans them.
>
> Background flush is already cleaning old or expired inodes first but the
> expire time is too far in the future at the time of page reclaim. To mitigate
> future problems, this patch wakes flusher threads to clean 4M of data -
> an amount that should be manageable without causing congestion in many cases.
>
> Ideally, the background flushers would only be cleaning pages belonging
> to the zone being scanned but it's not clear if this would be of benefit
> (less IO) or not (potentially less efficient IO if an inode is scattered
> across multiple zones).
>
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> ---
> mm/vmscan.c | 33 +++++++++++++++++++++++++++++++--
> 1 files changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 2d2b588..c4c81bc 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -142,6 +142,18 @@ static DECLARE_RWSEM(shrinker_rwsem);
> /* Direct lumpy reclaim waits up to five seconds for background cleaning */
> #define MAX_SWAP_CLEAN_WAIT 50
>
> +/*
> + * When reclaim encounters dirty data, wakeup flusher threads to clean
> + * a maximum of 4M of data.
> + */
> +#define MAX_WRITEBACK (4194304UL >> PAGE_SHIFT)
> +#define WRITEBACK_FACTOR (MAX_WRITEBACK / SWAP_CLUSTER_MAX)
> +static inline long nr_writeback_pages(unsigned long nr_dirty)
> +{
> + return laptop_mode ? 0 :
> + min(MAX_WRITEBACK, (nr_dirty * WRITEBACK_FACTOR));
> +}
??
As far as I remembered, Hannes pointed out wakeup_flusher_threads(0) is
incorrect. can you fix this?
> +
> static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
> struct scan_control *sc)
> {
> @@ -649,12 +661,14 @@ 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,
> + int file,
> unsigned long *nr_still_dirty)
> {
> LIST_HEAD(ret_pages);
> LIST_HEAD(free_pages);
> int pgactivate = 0;
> unsigned long nr_dirty = 0;
> + unsigned long nr_dirty_seen = 0;
> unsigned long nr_reclaimed = 0;
>
> cond_resched();
> @@ -748,6 +762,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> }
>
> if (PageDirty(page)) {
> + nr_dirty_seen++;
> +
> /*
> * Only kswapd can writeback filesystem pages to
> * avoid risk of stack overflow
> @@ -875,6 +891,18 @@ keep:
>
> list_splice(&ret_pages, page_list);
>
> + /*
> + * If reclaim is encountering dirty pages, it may be because
> + * dirty pages are reaching the end of the LRU even though the
> + * dirty_ratio may be satisified. In this case, wake flusher
> + * threads to pro-actively clean up to a maximum of
> + * 4 * SWAP_CLUSTER_MAX amount of data (usually 1/2MB) unless
> + * !may_writepage indicates that this is a direct reclaimer in
> + * laptop mode avoiding disk spin-ups
> + */
> + if (file && nr_dirty_seen && sc->may_writepage)
> + wakeup_flusher_threads(nr_writeback_pages(nr_dirty));
Umm..
I don't think this guessing is so acculate. following is brief of
current isolate_lru_pages().
static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
struct list_head *src, struct list_head *dst,
unsigned long *scanned, int order, int mode, int file)
{
for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
__isolate_lru_page(page, mode, file))
if (!order)
continue;
/*
* Attempt to take all pages in the order aligned region
* surrounding the tag page. Only take those pages of
* the same active state as that tag page. We may safely
* round the target page pfn down to the requested order
* as the mem_map is guarenteed valid out to MAX_ORDER,
* where that page is in a different zone we will detect
* it from its zone id and abort this block scan.
*/
for (; pfn < end_pfn; pfn++) {
struct page *cursor_page;
(snip)
}
(This was unchanged since initial lumpy reclaim commit)
That said, merely order-1 isolate_lru_pages(ISOLATE_INACTIVE) makes pfn
neighbor search. then, we might found dirty pages even though the page
don't stay in end of lru.
What do you think?
> +
> *nr_still_dirty = nr_dirty;
> count_vm_events(PGACTIVATE, pgactivate);
> return nr_reclaimed;
> @@ -1315,7 +1343,7 @@ 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_dirty);
> + file, &nr_dirty);
>
> /*
> * If specific pages are needed such as with direct reclaiming
> @@ -1351,7 +1379,8 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
> count_vm_events(PGDEACTIVATE, nr_active);
>
> nr_reclaimed += shrink_page_list(&page_list, sc,
> - PAGEOUT_IO_SYNC, &nr_dirty);
> + PAGEOUT_IO_SYNC, file,
> + &nr_dirty);
> }
> }
>
> --
> 1.7.1
>
--
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