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Date: Wed, 18 Jun 2008 20:36:52 +0900
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: kosaki.motohiro@...fujitsu.com,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
Andrew Morton <akpm@...ux-foundation.org>,
Rik van Riel <riel@...hat.com>,
Lee Schermerhorn <lee.schermerhorn@...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
Hi kame-san,
> putback_lru_page() in this patch has a new concepts.
> When it adds page to unevictable list, it checks the status is
> changed or not again. if changed, retry to putback.
it seems good idea :)
this patch can reduce lock_page() call.
> - } else if (page_evictable(page, NULL)) {
> - /*
> - * For evictable pages, we can use the cache.
> - * In event of a race, worst case is we end up with an
> - * unevictable page on [in]active list.
> - * We know how to handle that.
> - */
I think this comment is useful.
Why do you want kill it?
> +redo:
> + lru = !!TestClearPageActive(page);
> + if (page_evictable(page, NULL)) {
> lru += page_is_file_cache(page);
> lru_cache_add_lru(page, lru);
> - mem_cgroup_move_lists(page, lru);
> -#ifdef CONFIG_UNEVICTABLE_LRU
> - if (was_unevictable)
> - count_vm_event(NORECL_PGRESCUED);
> -#endif
> } else {
> - /*
> - * Put unevictable pages directly on zone's unevictable
> - * list.
> - */
ditto.
> + lru = LRU_UNEVICTABLE;
> add_page_to_unevictable_list(page);
> - mem_cgroup_move_lists(page, LRU_UNEVICTABLE);
> -#ifdef CONFIG_UNEVICTABLE_LRU
> - if (!was_unevictable)
> - count_vm_event(NORECL_PGCULLED);
> -#endif
> }
> + mem_cgroup_move_lists(page, lru);
> +
> + /*
> + * page's status can change while we move it among lru. If an evictable
> + * page is on unevictable list, it never be freed. To avoid that,
> + * check after we added it to the list, again.
> + */
> + if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
> + if (!isolate_lru_page(page)) {
> + put_page(page);
> + goto redo;
No.
We should treat carefully unevictable -> unevictable moving too.
> + }
> + /* This means someone else dropped this page from LRU
> + * So, it will be freed or putback to LRU again. There is
> + * nothing to do here.
> + */
> + }
> +
> + if (was_unevictable && lru != LRU_UNEVICTABLE)
> + count_vm_event(NORECL_PGRESCUED);
> + else if (!was_unevictable && lru == LRU_UNEVICTABLE)
> + count_vm_event(NORECL_PGCULLED);
>
> put_page(page); /* drop ref from isolate */
> - return ret; /* ret => "page still locked" */
> }
> -
> -/*
> - * Cull page that shrink_*_list() has detected to be unevictable
> - * under page lock to close races with other tasks that might be making
> - * the page evictable. Avoid stranding an evictable page on the
> - * unevictable list.
> - */
> -static void cull_unevictable_page(struct page *page)
> +#else
> +void putback_lru_page(struct page *page)
> {
> - lock_page(page);
> - if (putback_lru_page(page))
> - unlock_page(page);
> + int lru;
> + VM_BUG_ON(PageLRU(page));
> +
> + lru = !!TestClearPageActive(page) + page_is_file_cache(page);
> + lru_cache_add_lru(page, lru);
> + mem_cgroup_move_lists(page, lru);
> + put_page(page);
> }
> +#endif
>
> /*
> * shrink_page_list() returns the number of reclaimed pages
> @@ -746,8 +736,8 @@ free_it:
> continue;
>
> cull_mlocked:
> - if (putback_lru_page(page))
> - unlock_page(page);
> + unlock_page(page);
> + putback_lru_page(page);
> continue;
>
> activate_locked:
> @@ -1127,7 +1117,7 @@ static unsigned long shrink_inactive_lis
> list_del(&page->lru);
> if (unlikely(!page_evictable(page, NULL))) {
> spin_unlock_irq(&zone->lru_lock);
> - cull_unevictable_page(page);
> + putback_lru_page(page);
> spin_lock_irq(&zone->lru_lock);
> continue;
> }
> @@ -1231,7 +1221,7 @@ static void shrink_active_list(unsigned
> list_del(&page->lru);
>
> if (unlikely(!page_evictable(page, NULL))) {
> - cull_unevictable_page(page);
> + putback_lru_page(page);
> continue;
> }
>
> @@ -2393,8 +2383,6 @@ int zone_reclaim(struct zone *zone, gfp_
> int page_evictable(struct page *page, struct vm_area_struct *vma)
> {
>
> - VM_BUG_ON(PageUnevictable(page));
> -
> if (mapping_unevictable(page_mapping(page)))
> return 0;
Why do you remove this?
> @@ -169,7 +166,8 @@ static int __mlock_vma_pages_range(struc
>
> /*
> * get_user_pages makes pages present if we are
> - * setting mlock.
> + * setting mlock. and this extra reference count will
> + * disable migration of this page.
> */
> ret = get_user_pages(current, mm, addr,
> min_t(int, nr_pages, ARRAY_SIZE(pages)),
> @@ -197,14 +195,8 @@ static int __mlock_vma_pages_range(struc
> for (i = 0; i < ret; i++) {
> struct page *page = pages[i];
>
> - /*
> - * page might be truncated or migrated out from under
> - * us. Check after acquiring page lock.
> - */
> - lock_page(page);
> - if (page->mapping)
> + if (page_mapcount(page))
> mlock_vma_page(page);
> - unlock_page(page);
> put_page(page); /* ref from get_user_pages() */
>
> /*
> @@ -240,6 +232,9 @@ static int __munlock_pte_handler(pte_t *
> struct page *page;
> pte_t pte;
>
> + /*
> + * page is never be unmapped by page-reclaim. we lock this page now.
> + */
> retry:
> pte = *ptep;
> /*
> @@ -261,7 +256,15 @@ retry:
> goto out;
>
> lock_page(page);
> - if (!page->mapping) {
> + /*
> + * Because we lock page here, we have to check 2 cases.
> + * - the page is migrated.
> + * - the page is truncated (file-cache only)
> + * Note: Anonymous page doesn't clear page->mapping even if it
> + * is removed from rmap.
> + */
> + if (!page->mapping ||
> + (PageAnon(page) && !page_mapcount(page))) {
> unlock_page(page);
> goto retry;
> }
> Index: test-2.6.26-rc5-mm3/mm/migrate.c
> ===================================================================
> --- test-2.6.26-rc5-mm3.orig/mm/migrate.c
> +++ test-2.6.26-rc5-mm3/mm/migrate.c
> @@ -67,9 +67,7 @@ int putback_lru_pages(struct list_head *
>
> list_for_each_entry_safe(page, page2, l, lru) {
> list_del(&page->lru);
> - lock_page(page);
> - if (putback_lru_page(page))
> - unlock_page(page);
> + putback_lru_page(page);
> count++;
> }
> return count;
> @@ -571,7 +569,6 @@ static int fallback_migrate_page(struct
> static int move_to_new_page(struct page *newpage, struct page *page)
> {
> struct address_space *mapping;
> - int unlock = 1;
> int rc;
>
> /*
> @@ -610,12 +607,11 @@ static int move_to_new_page(struct page
> * Put back on LRU while holding page locked to
> * handle potential race with, e.g., munlock()
> */
this comment isn't true.
> - unlock = putback_lru_page(newpage);
> + putback_lru_page(newpage);
> } else
> newpage->mapping = NULL;
originally move_to_lru() called in unmap_and_move().
unevictable infrastructure patch move to this point for
calling putback_lru_page() under page locked.
So, your patch remove page locked dependency.
move to unmap_and_move() again is better.
it become page lock holding time reducing.
>
> - if (unlock)
> - unlock_page(newpage);
> + unlock_page(newpage);
>
> return rc;
> }
> @@ -632,7 +628,6 @@ static int unmap_and_move(new_page_t get
> struct page *newpage = get_new_page(page, private, &result);
> int rcu_locked = 0;
> int charge = 0;
> - int unlock = 1;
>
> if (!newpage)
> return -ENOMEM;
> @@ -713,6 +708,7 @@ rcu_unlock:
> rcu_read_unlock();
>
> unlock:
> + unlock_page(page);
>
> if (rc != -EAGAIN) {
> /*
> @@ -722,18 +718,9 @@ unlock:
> * restored.
> */
> list_del(&page->lru);
> - if (!page->mapping) {
> - VM_BUG_ON(page_count(page) != 1);
> - unlock_page(page);
> - put_page(page); /* just free the old page */
> - goto end_migration;
> - } else
> - unlock = putback_lru_page(page);
> + putback_lru_page(page);
> }
>
> - if (unlock)
> - unlock_page(page);
> -
> end_migration:
> if (!charge)
> mem_cgroup_end_migration(newpage);
> Index: test-2.6.26-rc5-mm3/mm/internal.h
> ===================================================================
> --- test-2.6.26-rc5-mm3.orig/mm/internal.h
> +++ test-2.6.26-rc5-mm3/mm/internal.h
> @@ -43,7 +43,7 @@ static inline void __put_page(struct pag
> * in mm/vmscan.c:
> */
> extern int isolate_lru_page(struct page *page);
> -extern int putback_lru_page(struct page *page);
> +extern void putback_lru_page(struct page *page);
>
> /*
> * in mm/page_alloc.c
>
--
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