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b=EWJTtxytujM8XiQY/uBZg3PX0H07/smcJ/DzloEwktMR/kvYpRnN7+SOboNqCjqqh wYfDZDFGPbKXQPCcTlbj/fX6q5RFvSKVV3fE11c8HbcdyF4DKfcF6yX/m0KM7KXX1G ijrzbFrwwwKDwAuk9vMAj44ktqJxvVUmoyTIhzfY= Date: Mon, 8 Jul 2024 15:16:19 -0700 From: Andrew Morton To: Yu Zhao Cc: Bharata B Rao , "Matthew Wilcox (Oracle)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman , Johannes Weiner Subject: Re: [PATCH mm-unstable v1] mm/truncate: batch-clear shadow entries Message-Id: <20240708151619.dc738d16d3b2d56d6c4fe285@linux-foundation.org> In-Reply-To: <20240708212753.3120511-1-yuzhao@google.com> References: <20240708212753.3120511-1-yuzhao@google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 9E1624000B X-Stat-Signature: 4jsactdpcm99t6i163ofier5m138pzr6 X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1720476984-821140 X-HE-Meta: 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 v+LomFCN 9u1UG7yQ3giv7ZgkywIRX6Boeo/hXUsudbbYU1TbGFppReXya92mv3c0CyYKHyor2LoJkvrAo4LznvcGSjGacwUnBzytMibnlGY95hZ9+5+MamHp/Xmp3XkELoujzV7X9k1Ivpcy6HOWiLhLIVCO3iK3rjoz5CdJ+/jjM1Qk0041OmwMQ6+F4zJib2hSK7JOJeV9pe1q2bOyKoZ/2UEY+kZxpW8pE2e6K//wpdpp6HKK4v0r9SVo/iZc9Og== 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 Mon, 8 Jul 2024 15:27:53 -0600 Yu Zhao wrote: > Make clear_shadow_entry() clear shadow entries in `struct folio_batch` > so that it can reduce contention on i_lock and i_pages locks, e.g., > > watchdog: BUG: soft lockup - CPU#29 stuck for 11s! [fio:2701649] > clear_shadow_entry+0x3d/0x100 > mapping_try_invalidate+0x117/0x1d0 > invalidate_mapping_pages+0x10/0x20 > invalidate_bdev+0x3c/0x50 > blkdev_common_ioctl+0x5f7/0xa90 > blkdev_ioctl+0x109/0x270 This will clearly reduce lock traffic a lot, but does it truly fix the issue? Is it the case that sufficiently extreme loads will still run into problems? > --- a/mm/truncate.c > +++ b/mm/truncate.c > @@ -39,12 +39,24 @@ static inline void __clear_shadow_entry(struct address_space *mapping, > xas_store(&xas, NULL); > } > > -static void clear_shadow_entry(struct address_space *mapping, pgoff_t index, > - void *entry) > +static void clear_shadow_entry(struct address_space *mapping, > + struct folio_batch *fbatch, pgoff_t *indices) > { > + int i; > + > + if (shmem_mapping(mapping) || dax_mapping(mapping)) > + return; We lost the comment which was in invalidate_exceptional_entry() and elsewhere. It wasn't a terribly good one but I do think a few words which explain why we're testing for these things would be helpful. I expect we should backport this. But identifying a Fixes: target looks to be challenging.