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Message-Id: <1213981843.6474.68.camel@lts-notebook>
Date: Fri, 20 Jun 2008 13:10:43 -0400
From: Lee Schermerhorn <Lee.Schermerhorn@...com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
Andrew Morton <akpm@...ux-foundation.org>,
Rik van Riel <riel@...hat.com>,
Kosaki Motohiro <kosaki.motohiro@...fujitsu.com>,
Nick Piggin <npiggin@...e.de>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org
Subject: Re: [Experimental][PATCH] putback_lru_page rework
On Fri, 2008-06-20 at 10:13 +0900, KAMEZAWA Hiroyuki wrote:
> Lee-san, this is an additonal one..
> Not-tested-yet, just by review.
OK, I'll test this on my x86_64 platform, which doesn't seem to hit the
soft lockups.
>
> Fixing page_lock() <-> zone->lock nesting of bad-behavior.
>
> Before:
> lock_page()(TestSetPageLocked())
> spin_lock(zone->lock)
> unlock_page()
> spin_unlock(zone->lock)
Couple of comments:
* I believe that the locks are acquired in the right order--at least as
documented in the comments in mm/rmap.c.
* The unlocking appears out of order because this function attempts to
hold the zone lock across a few pages in the pagevec, but must switch to
a different zone lru lock when it finds a page on a different zone from
the zone whose lock it is holding--like in the pagevec draining
functions, altho' they don't need to lock the page.
> After:
> spin_lock(zone->lock)
> spin_unlock(zone->lock)
Right. With your reworked check_move_unevictable_page() [with retry],
we don't need to lock the page here, any more. That means we can revert
all of the changes to pass the mapping back to sys_shmctl() and move the
call to scan_mapping_unevictable_pages() back to shmem_lock() after
clearing the address_space's unevictable flag. We only did that to
avoid sleeping while holding the shmem_inode_info lock and the
shmid_kernel's ipc_perm spinlock.
Shall I handle that, after we've tested this patch?
>
> Including nit-pick fix. (I'll ask Kosaki-san to merge this to his 5/5)
>
> Hmm...
>
> ---
> mm/vmscan.c | 25 +++++--------------------
> 1 file changed, 5 insertions(+), 20 deletions(-)
>
> Index: test-2.6.26-rc5-mm3/mm/vmscan.c
> ===================================================================
> --- test-2.6.26-rc5-mm3.orig/mm/vmscan.c
> +++ test-2.6.26-rc5-mm3/mm/vmscan.c
> @@ -1106,7 +1106,7 @@ static unsigned long shrink_inactive_lis
> if (nr_taken == 0)
> goto done;
>
> - spin_lock(&zone->lru_lock);
> + spin_lock_irq(&zone->lru_lock);
1) It appears that the spin_lock() [no '_irq'] was there because irqs
are disabled a few lines above so that we could use non-atomic
__count[_zone]_vm_events().
2) I think this predates the split lru or unevictable lru patches, so
these changes are unrelated.
> /*
> * Put back any unfreeable pages.
> */
> @@ -1136,9 +1136,8 @@ static unsigned long shrink_inactive_lis
> }
> }
> } while (nr_scanned < max_scan);
> - spin_unlock(&zone->lru_lock);
> + spin_unlock_irq(&zone->lru_lock);
> done:
> - local_irq_enable();
> pagevec_release(&pvec);
> return nr_reclaimed;
> }
> @@ -2438,7 +2437,7 @@ static void show_page_path(struct page *
> */
> static void check_move_unevictable_page(struct page *page, struct zone *zone)
> {
> -
> +retry:
> ClearPageUnevictable(page); /* for page_evictable() */
We can remove this comment ^^^^^^^^^^^^^^^^^^^^^^^^^^
page_evictable() no longer asserts !PageUnevictable(), right?
> if (page_evictable(page, NULL)) {
> enum lru_list l = LRU_INACTIVE_ANON + page_is_file_cache(page);
> @@ -2455,6 +2454,8 @@ static void check_move_unevictable_page(
> */
> SetPageUnevictable(page);
> list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
> + if (page_evictable(page, NULL))
> + goto retry;
> }
> }
>
> @@ -2494,16 +2495,6 @@ void scan_mapping_unevictable_pages(stru
> next = page_index;
> next++;
>
> - if (TestSetPageLocked(page)) {
> - /*
> - * OK, let's do it the hard way...
> - */
> - if (zone)
> - spin_unlock_irq(&zone->lru_lock);
> - zone = NULL;
> - lock_page(page);
> - }
> -
> if (pagezone != zone) {
> if (zone)
> spin_unlock_irq(&zone->lru_lock);
> @@ -2514,8 +2505,6 @@ void scan_mapping_unevictable_pages(stru
> if (PageLRU(page) && PageUnevictable(page))
> check_move_unevictable_page(page, zone);
>
> - unlock_page(page);
> -
> }
> if (zone)
> spin_unlock_irq(&zone->lru_lock);
> @@ -2551,15 +2540,11 @@ void scan_zone_unevictable_pages(struct
> for (scan = 0; scan < batch_size; scan++) {
> struct page *page = lru_to_page(l_unevictable);
>
> - if (TestSetPageLocked(page))
> - continue;
> -
> prefetchw_prev_lru_page(page, l_unevictable, flags);
>
> if (likely(PageLRU(page) && PageUnevictable(page)))
> check_move_unevictable_page(page, zone);
>
> - unlock_page(page);
> }
> spin_unlock_irq(&zone->lru_lock);
>
>
I'll let you know how it goes.
Later,
Lee
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