| Message ID | 3eafa969-5b1a-accf-88fe-318784c791a@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [mmotm,v2] mm: delete __ClearPageWaiters() | expand |
On 04.03.22 22:25, Hugh Dickins wrote: > The PG_waiters bit is not included in PAGE_FLAGS_CHECK_AT_FREE, and > vmscan.c's free_unref_page_list() callers rely on that not to generate > bad_page() alerts. So __page_cache_release(), put_pages_list() and > release_pages() (and presumably copy-and-pasted free_zone_device_page()) > are redundant and misleading to make a special point of clearing it (as > the "__" implies, it could only safely be used on the freeing path). > > Delete __ClearPageWaiters(). Remark on this in one of the "possible" > comments in folio_wake_bit(), and delete the superfluous comments. > > Signed-off-by: Hugh Dickins <hughd@google.com> > Tested-by: Yu Zhao <yuzhao@google.com> Thanks Reviewed-by: David Hildenbrand <david@redhat.com>
On Fri, Mar 4, 2022 at 1:25 PM Hugh Dickins <hughd@google.com> wrote: > > The PG_waiters bit is not included in PAGE_FLAGS_CHECK_AT_FREE, and > vmscan.c's free_unref_page_list() callers rely on that not to generate > bad_page() alerts. So __page_cache_release(), put_pages_list() and > release_pages() (and presumably copy-and-pasted free_zone_device_page()) > are redundant and misleading to make a special point of clearing it (as > the "__" implies, it could only safely be used on the freeing path). > > Delete __ClearPageWaiters(). Remark on this in one of the "possible" > comments in folio_wake_bit(), and delete the superfluous comments. > > Signed-off-by: Hugh Dickins <hughd@google.com> > Tested-by: Yu Zhao <yuzhao@google.com> > --- > v2: Add Tested-by from Yu Zhao. > Update to latest function names in the commit message. > Reword comment in folio_wake_bit() per David Hildenbrand. Reviewed-by: Yang Shi <shy828301@gmail.com> > > include/linux/page-flags.h | 2 +- > mm/filemap.c | 23 ++++++++--------------- > mm/memremap.c | 2 -- > mm/swap.c | 4 ---- > 4 files changed, 9 insertions(+), 22 deletions(-) > > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -481,7 +481,7 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n) > TESTSETFLAG_FALSE(uname, lname) TESTCLEARFLAG_FALSE(uname, lname) > > __PAGEFLAG(Locked, locked, PF_NO_TAIL) > -PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) __CLEARPAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) > +PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) > PAGEFLAG(Error, error, PF_NO_TAIL) TESTCLEARFLAG(Error, error, PF_NO_TAIL) > PAGEFLAG(Referenced, referenced, PF_HEAD) > TESTCLEARFLAG(Referenced, referenced, PF_HEAD) > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -1179,24 +1179,17 @@ static void folio_wake_bit(struct folio *folio, int bit_nr) > } > > /* > - * It is possible for other pages to have collided on the waitqueue > - * hash, so in that case check for a page match. That prevents a long- > - * term waiter > + * It's possible to miss clearing waiters here, when we woke our page > + * waiters, but the hashed waitqueue has waiters for other pages on it. > + * That's okay, it's a rare case. The next waker will clear it. > * > - * It is still possible to miss a case here, when we woke page waiters > - * and removed them from the waitqueue, but there are still other > - * page waiters. > + * Note that, depending on the page pool (buddy, hugetlb, ZONE_DEVICE, > + * other), the flag may be cleared in the course of freeing the page; > + * but that is not required for correctness. > */ > - if (!waitqueue_active(q) || !key.page_match) { > + if (!waitqueue_active(q) || !key.page_match) > folio_clear_waiters(folio); > - /* > - * It's possible to miss clearing Waiters here, when we woke > - * our page waiters, but the hashed waitqueue has waiters for > - * other pages on it. > - * > - * That's okay, it's a rare case. The next waker will clear it. > - */ > - } > + > spin_unlock_irqrestore(&q->lock, flags); > } > > --- a/mm/memremap.c > +++ b/mm/memremap.c > @@ -487,8 +487,6 @@ void free_zone_device_page(struct page *page) > if (WARN_ON_ONCE(!page->pgmap->ops || !page->pgmap->ops->page_free)) > return; > > - __ClearPageWaiters(page); > - > mem_cgroup_uncharge(page_folio(page)); > > /* > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -97,7 +97,6 @@ static void __page_cache_release(struct page *page) > mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages); > count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages); > } > - __ClearPageWaiters(page); > } > > static void __put_single_page(struct page *page) > @@ -152,7 +151,6 @@ void put_pages_list(struct list_head *pages) > continue; > } > /* Cannot be PageLRU because it's passed to us using the lru */ > - __ClearPageWaiters(page); > } > > free_unref_page_list(pages); > @@ -966,8 +964,6 @@ void release_pages(struct page **pages, int nr) > count_vm_event(UNEVICTABLE_PGCLEARED); > } > > - __ClearPageWaiters(page); > - > list_add(&page->lru, &pages_to_free); > } > if (lruvec)
--- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -481,7 +481,7 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n) TESTSETFLAG_FALSE(uname, lname) TESTCLEARFLAG_FALSE(uname, lname) __PAGEFLAG(Locked, locked, PF_NO_TAIL) -PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) __CLEARPAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) +PAGEFLAG(Waiters, waiters, PF_ONLY_HEAD) PAGEFLAG(Error, error, PF_NO_TAIL) TESTCLEARFLAG(Error, error, PF_NO_TAIL) PAGEFLAG(Referenced, referenced, PF_HEAD) TESTCLEARFLAG(Referenced, referenced, PF_HEAD) --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1179,24 +1179,17 @@ static void folio_wake_bit(struct folio *folio, int bit_nr) } /* - * It is possible for other pages to have collided on the waitqueue - * hash, so in that case check for a page match. That prevents a long- - * term waiter + * It's possible to miss clearing waiters here, when we woke our page + * waiters, but the hashed waitqueue has waiters for other pages on it. + * That's okay, it's a rare case. The next waker will clear it. * - * It is still possible to miss a case here, when we woke page waiters - * and removed them from the waitqueue, but there are still other - * page waiters. + * Note that, depending on the page pool (buddy, hugetlb, ZONE_DEVICE, + * other), the flag may be cleared in the course of freeing the page; + * but that is not required for correctness. */ - if (!waitqueue_active(q) || !key.page_match) { + if (!waitqueue_active(q) || !key.page_match) folio_clear_waiters(folio); - /* - * It's possible to miss clearing Waiters here, when we woke - * our page waiters, but the hashed waitqueue has waiters for - * other pages on it. - * - * That's okay, it's a rare case. The next waker will clear it. - */ - } + spin_unlock_irqrestore(&q->lock, flags); } --- a/mm/memremap.c +++ b/mm/memremap.c @@ -487,8 +487,6 @@ void free_zone_device_page(struct page *page) if (WARN_ON_ONCE(!page->pgmap->ops || !page->pgmap->ops->page_free)) return; - __ClearPageWaiters(page); - mem_cgroup_uncharge(page_folio(page)); /* --- a/mm/swap.c +++ b/mm/swap.c @@ -97,7 +97,6 @@ static void __page_cache_release(struct page *page) mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages); count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages); } - __ClearPageWaiters(page); } static void __put_single_page(struct page *page) @@ -152,7 +151,6 @@ void put_pages_list(struct list_head *pages) continue; } /* Cannot be PageLRU because it's passed to us using the lru */ - __ClearPageWaiters(page); } free_unref_page_list(pages); @@ -966,8 +964,6 @@ void release_pages(struct page **pages, int nr) count_vm_event(UNEVICTABLE_PGCLEARED); } - __ClearPageWaiters(page); - list_add(&page->lru, &pages_to_free); } if (lruvec)