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Message-ID: <20101129165706.GH13268@csn.ul.ie>
Date: Mon, 29 Nov 2010 16:57:06 +0000
From: Mel Gorman <mel@....ul.ie>
To: Minchan Kim <minchan.kim@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
Ben Gamari <bgamari.foss@...il.com>,
Wu Fengguang <fengguang.wu@...el.com>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Johannes Weiner <hannes@...xchg.org>,
Nick Piggin <npiggin@...nel.dk>
Subject: Re: [PATCH 2/3] Reclaim invalidated page ASAP
On Tue, Nov 30, 2010 at 12:23:20AM +0900, Minchan Kim wrote:
> invalidate_mapping_pages is very big hint to reclaimer.
> It means user doesn't want to use the page any more.
> So in order to prevent working set page eviction, this patch
> move the page into tail of inactive list by PG_reclaim.
>
> Please, remember that pages in inactive list are working set
> as well as active list. If we don't move pages into inactive list's
> tail, pages near by tail of inactive list can be evicted although
> we have a big clue about useless pages. It's totally bad.
>
> Now PG_readahead/PG_reclaim is shared.
> fe3cba17 added ClearPageReclaim into clear_page_dirty_for_io for
> preventing fast reclaiming readahead marker page.
>
> In this series, PG_reclaim is used by invalidated page, too.
> If VM find the page is invalidated and it's dirty, it sets PG_reclaim
> to reclaim asap. Then, when the dirty page will be writeback,
> clear_page_dirty_for_io will clear PG_reclaim unconditionally.
> It disturbs this serie's goal.
>
> I think it's okay to clear PG_readahead when the page is dirty, not
> writeback time. So this patch moves ClearPageReadahead.
>
> Signed-off-by: Minchan Kim <minchan.kim@...il.com>
> Acked-by: Rik van Riel <riel@...hat.com>
> Cc: Wu Fengguang <fengguang.wu@...el.com>
> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Nick Piggin <npiggin@...nel.dk>
> Cc: Mel Gorman <mel@....ul.ie>
>
> Changelog since v2:
> - put ClearPageReclaim in set_page_dirty - suggested by Wu.
>
> Changelog since v1:
> - make the invalidated page reclaim asap - suggested by Andrew.
> ---
> mm/page-writeback.c | 12 +++++++++++-
> mm/swap.c | 48 +++++++++++++++++++++++++++++++++++-------------
> 2 files changed, 46 insertions(+), 14 deletions(-)
>
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index fc93802..88587a5 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1250,6 +1250,17 @@ int set_page_dirty(struct page *page)
> {
> struct address_space *mapping = page_mapping(page);
>
> + /*
> + * readahead/lru_deactivate_page could remain
> + * PG_readahead/PG_reclaim due to race with end_page_writeback
> + * About readahead, if the page is written, the flags would be
> + * reset. So no problem.
> + * About lru_deactivate_page, if the page is redirty, the flag
> + * will be reset. So no problem. but if the page is used by readahead
> + * it will confuse readahead and make it restart the size rampup
> + * process. But it's a trivial problem.
> + */
> + ClearPageReclaim(page);
> if (likely(mapping)) {
> int (*spd)(struct page *) = mapping->a_ops->set_page_dirty;
> #ifdef CONFIG_BLOCK
> @@ -1307,7 +1318,6 @@ int clear_page_dirty_for_io(struct page *page)
>
> BUG_ON(!PageLocked(page));
>
> - ClearPageReclaim(page);
> if (mapping && mapping_cap_account_dirty(mapping)) {
> /*
> * Yes, Virginia, this is indeed insane.
> diff --git a/mm/swap.c b/mm/swap.c
> index 19e0812..936b281 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -275,28 +275,50 @@ void add_page_to_unevictable_list(struct page *page)
> * into inative list's head. Because the VM expects the page would
> * be writeout by flusher. The flusher's writeout is much effective
> * than reclaimer's random writeout.
> + *
> + * If the page isn't page_mapped and dirty/writeback, the page
> + * could reclaim asap using PG_reclaim.
> + *
> + * 1. active, mapped page -> none
> + * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
> + * 3. inactive, mapped page -> none
> + * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
> + * 5. Others -> none
> + *
> + * In 4, why it moves inactive's head, the VM expects the page would
> + * be writeout by flusher. The flusher's writeout is much effective than
> + * reclaimer's random writeout.
> */
> static void __lru_deactivate(struct page *page, struct zone *zone)
> {
> int lru, file;
> - unsigned long vm_flags;
> + int active = 0;
>
> - if (!PageLRU(page) || !PageActive(page))
> + if (!PageLRU(page))
> return;
> -
> /* Some processes are using the page */
> if (page_mapped(page))
> return;
> -
> - file = page_is_file_cache(page);
> - lru = page_lru_base_type(page);
> - del_page_from_lru_list(zone, page, lru + LRU_ACTIVE);
> - ClearPageActive(page);
> - ClearPageReferenced(page);
> - add_page_to_lru_list(zone, page, lru);
> - __count_vm_event(PGDEACTIVATE);
> -
> - update_page_reclaim_stat(zone, page, file, 0);
> + if (PageActive(page))
> + active = 1;
> +
> + if (PageWriteback(page) || PageDirty(page)) {
> + /*
> + * PG_reclaim could be raced with end_page_writeback
> + * It can make readahead confusing. But race window
> + * is _really_ small and it's non-critical problem.
> + */
> + SetPageReclaim(page);
> +
> + file = page_is_file_cache(page);
> + lru = page_lru_base_type(page);
> + del_page_from_lru_list(zone, page, lru + active);
> + ClearPageActive(page);
> + ClearPageReferenced(page);
> + add_page_to_lru_list(zone, page, lru);
> + __count_vm_event(PGDEACTIVATE);
You update PGDEACTIVATE whether the page was active or not.
> + update_page_reclaim_stat(zone, page, file, 0);
> + }
> }
>
> /*
> --
> 1.7.0.4
>
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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