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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tcSP9-00000009fxz-44xx; Mon, 27 Jan 2025 16:56:08 +0000 Date: Mon, 27 Jan 2025 16:56:07 +0000 From: Matthew Wilcox To: David Hildenbrand Cc: linux-mm@kvack.org, linux-block@vger.kernel.org, Muchun Song , Jane Chu , Andres Freund Subject: Re: Direct I/O performance problems with 1GB pages Message-ID: References: <503c29c8-bcc7-4a6c-ab2e-ebf238a9a1db@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <503c29c8-bcc7-4a6c-ab2e-ebf238a9a1db@redhat.com> X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: AFF8C40013 X-Stat-Signature: ohppgj6wzx94r75a43fz3kdb7fdiei3q X-Rspam-User: X-HE-Tag: 1737996970-128172 X-HE-Meta: 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 vbKYI6n/ vU09kJBrniX0yN65kBnMprUBuKcashWF1t8RH2/9RkK53vfq2YF26yefbQhnuDJZSYvgICz0BvmJ0divQS2yM+sRYescPe5YLNHIp5OVvPBVAkr8Thg4xtlgYasqVJPEQMZ6ORWT1oRCTTeh8QWCLsIccaW8VqXLBt/9yf4nEdjPHb9i2x2ArQNS2DmZBmLF9qlfk3wgioFK72NLTwR6sXt0QUPGTR63S7DtF 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, Jan 27, 2025 at 05:20:25PM +0100, David Hildenbrand wrote: > > > 14.04% postgres [kernel.kallsyms] [k] try_grab_folio_fast > > > | > > > --14.04%--try_grab_folio_fast > > > gup_fast_fallback > > > | > > > --13.85%--iov_iter_extract_pages > > > bio_iov_iter_get_pages > > > iomap_dio_bio_iter > > > __iomap_dio_rw > > > iomap_dio_rw > > > xfs_file_dio_read > > > xfs_file_read_iter > > > __io_read > > > io_read > > > io_issue_sqe > > > io_submit_sqes > > > __do_sys_io_uring_enter > > > do_syscall_64 > > BTW, two things that come to mind: > > > (1) We always fallback to GUP-slow, I wonder why. GUP-fast would go via > try_grab_folio_fast(). I don't think we do? iov_iter_extract_pages() calls iov_iter_extract_user_pages() calls pin_user_pages_fast() calls gup_fast_fallback() calls gup_fast() calls gup_fast_pgd_range() calls gup_fast_p4d_range() calls gup_fast_pud_range() calls gup_fast_pud_leaf() calls try_grab_folio_fast() which is where we see the contention. If that were to fail, we'd see contention in __get_user_pages_locked(), right?