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Date: Wed, 18 Jun 2008 20:55:40 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: 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
On Wed, 18 Jun 2008 20:36:52 +0900
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> 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.
>
yes.
>
> > - } 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?
>
Oh, my mistake.
> > + 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 lru is the destination ;)
>
> > + }
> > + /* 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?
>
I caught panci here ;)
maybe
==
if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL))
==
check is.
>
>
>
> > @@ -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.
>
yes.
> > - 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.
>
ok, will look into again.
Thanks,
-Kame
> >
> > - 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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