[{"id":3684667,"web_url":"http://patchwork.ozlabs.org/comment/3684667/","msgid":"","date":"2026-04-30T12:35:30","subject":"Re: [PATCH v2 4/5] mm: Don't retry page fault if folio is uptodate\n during swap-in","submitter":{"id":70855,"url":"http://patchwork.ozlabs.org/api/people/70855/","name":"Matthew Wilcox","email":"willy@infradead.org"},"content":"On Thu, Apr 30, 2026 at 12:04:26PM +0800, Barry Song (Xiaomi) wrote:\n> If we are waiting for long I/O to complete, it makes sense to\n> avoid holding locks for too long. However, if the folio is\n> uptodate, we are likely only waiting for a concurrent PTE\n> update to finish. Retrying the entire page fault seems\n> excessive.\n\nI think the idea is good, but the implementation is misplaced.\nThe check for folio_uptodate() should be inside folio_lock_or_retry()\nrather than tampering with FAULT_FLAG_ALLOW_RETRY in its caller.\n\nSimilarly for your next patch.\n\n> Signed-off-by: Barry Song (Xiaomi) \n> ---\n> mm/memory.c | 7 +++++++\n> 1 file changed, 7 insertions(+)\n> \n> diff --git a/mm/memory.c b/mm/memory.c\n> index 0c740ca363cc..a2e4f2d87ec8 100644\n> --- a/mm/memory.c\n> +++ b/mm/memory.c\n> @@ -4949,6 +4949,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)\n> \t}\n> \n> \tswapcache = folio;\n> +\t/*\n> +\t * If the folio is uptodate, we are likely only waiting for\n> +\t * another concurrent PTE mapping to complete, which should\n> +\t * be brief. No need to drop the lock and retry the fault.\n> +\t */\n> +\tif (folio_test_uptodate(folio))\n> +\t\tvmf->flags &= ~FAULT_FLAG_ALLOW_RETRY;\n> \tret |= folio_lock_or_retry(folio, vmf);\n> \tif (ret & VM_FAULT_RETRY) {\n> \t\tif (fault_flag_allow_retry_first(vmf->flags) &&\n> -- \n> 2.39.3 (Apple Git-146)\n> \n>","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n secure) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256\n header.s=casper.20170209 header.b=iAUflMNT;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=2404:9400:21b9:f100::1; helo=lists.ozlabs.org;\n envelope-from=linuxppc-dev+bounces-20342-incoming=patchwork.ozlabs.org@lists.ozlabs.org;\n receiver=patchwork.ozlabs.org)","lists.ozlabs.org;\n arc=none smtp.remote-ip=\"2001:8b0:10b:1236::1\"","lists.ozlabs.org;\n dmarc=fail (p=none dis=none) header.from=infradead.org","lists.ozlabs.org;\n spf=none (no SPF record) smtp.mailfrom=infradead.org\n (client-ip=2001:8b0:10b:1236::1; 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charset=us-ascii","Content-Disposition":"inline","In-Reply-To":"<20260430040427.4672-5-baohua@kernel.org>","X-Spam-Status":"No, score=-2.5 required=3.0 tests=DKIM_SIGNED,DKIM_VALID,\n\tDKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE,SPF_NONE\n\tautolearn=disabled version=4.0.1 OzLabs 8","X-Spam-Checker-Version":"SpamAssassin 4.0.1 (2024-03-25) on lists.ozlabs.org"}},{"id":3685166,"web_url":"http://patchwork.ozlabs.org/comment/3685166/","msgid":"","date":"2026-05-01T16:11:03","subject":"Re: [PATCH v2 4/5] mm: Don't retry page fault if folio is uptodate\n during swap-in","submitter":{"id":70855,"url":"http://patchwork.ozlabs.org/api/people/70855/","name":"Matthew Wilcox","email":"willy@infradead.org"},"content":"On Thu, Apr 30, 2026 at 01:35:30PM +0100, Matthew Wilcox wrote:\n> On Thu, Apr 30, 2026 at 12:04:26PM +0800, Barry Song (Xiaomi) wrote:\n> > If we are waiting for long I/O to complete, it makes sense to\n> > avoid holding locks for too long. However, if the folio is\n> > uptodate, we are likely only waiting for a concurrent PTE\n> > update to finish. Retrying the entire page fault seems\n> > excessive.\n> \n> I think the idea is good, but the implementation is misplaced.\n> The check for folio_uptodate() should be inside folio_lock_or_retry()\n> rather than tampering with FAULT_FLAG_ALLOW_RETRY in its caller.\n\nActually it needs to be a little more complex than this. We\nsometimes wait for writeback while holding the folio lock, and\nthat's a similar latency to reads (or with cheap NAND, maybe longer!)\n\nSo I think the test needs to be:\n\n\tif (folio_test_uptodate(folio) && !folio_test_writeback(folio))","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n secure) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256\n header.s=casper.20170209 header.b=S+PrOaTu;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=112.213.38.117; helo=lists.ozlabs.org;\n envelope-from=linuxppc-dev+bounces-20370-incoming=patchwork.ozlabs.org@lists.ozlabs.org;\n receiver=patchwork.ozlabs.org)","lists.ozlabs.org;\n arc=none smtp.remote-ip=\"2001:8b0:10b:1236::1\"","lists.ozlabs.org;\n dmarc=pass (p=none dis=none) header.from=infradead.org","lists.ozlabs.org;\n\tdkim=pass (2048-bit key;\n secure) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256\n header.s=casper.20170209 header.b=S+PrOaTu;\n\tdkim-atps=neutral","lists.ozlabs.org;\n spf=none (no SPF record) smtp.mailfrom=infradead.org\n (client-ip=2001:8b0:10b:1236::1; 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