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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: br913gyjt5rx4iw7zqwu3zcrw5ab8rcp X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: AEA3AA0002 X-Rspam-User: X-HE-Tag: 1708403451-393401 X-HE-Meta: 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 GuD1Pmnl 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/19/24 2:59 PM, Matthew Wilcox wrote: > On Sun, May 09, 2021 at 08:40:25PM +0100, Matthew Wilcox wrote: >> On Fri, Apr 30, 2021 at 09:50:29AM -0700, Linus Torvalds wrote: >>> On Thu, Apr 29, 2021 at 10:55 PM Andrew Morton >>> wrote: >>>> + rcu_read_lock(); >>>> + xas_for_each(&xas, page, max) { >>>> + if (xas_retry(&xas, page)) >>>> + continue; >>>> + if (xa_is_value(page)) >>>> + continue; >>>> + if (PageDirty(page) || PageLocked(page) || PageWriteback(page)) >>>> + break; >>>> + } >>>> + rcu_read_unlock(); >>> >>> Whee. This looks very very expensive indeed. >>> >>> Why is is going to each page, why does it care about locked when the >>> simple early cases did not? >> >> I was hoping Jens would answer this, but I guess he missed it so far. >> I don't know why it now cares about whether the page is locked or not. >> I presume it's not even the slightest bit slow for Jens because the >> common case is that there are no pages in the range, and so we never >> check any pages. > > Looking at this again, since the change to operate on folios, we're now > living dangerously as we don't have a reference on the folio, so it can > now be freed, turned into a tail page and trigger the VM_BUG_ON_PGFLAGS() > in folio_flags(). > > Rather than take a refcount on the folio to prevent that from happening, > we can just examine the pagecache flags in the XArray. like this. > Assuming there really isn't a need to check the locked flag (which for > obvious reasons we don't mirror into the xarray marks). > > Jens, WDYT? > > diff --git a/mm/filemap.c b/mm/filemap.c > index 750e779c23db..09f3851157f9 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -640,10 +640,8 @@ bool filemap_range_has_writeback(struct address_space *mapping, > xas_for_each(&xas, folio, max) { > if (xas_retry(&xas, folio)) > continue; > - if (xa_is_value(folio)) > - continue; > - if (folio_test_dirty(folio) || folio_test_locked(folio) || > - folio_test_writeback(folio)) > + if (xas_get_mark(&xas, PAGECACHE_TAG_DIRTY) || > + xas_get_mark(&xas, PAGECACHE_TAG_WRITEBACK)) > break; > } > rcu_read_unlock(); Blast from the past, guess I did miss it back then. This looks a lot more reasonable to me, also in terms of overhead, compared to the previous one. Heading out for the rest of the week tomorrow morning, but I can give it a test spin as well once I'm back. -- Jens Axboe