From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BC132C433DF for ; Mon, 1 Jun 2020 14:26:52 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6DAAC207D5 for ; Mon, 1 Jun 2020 14:26:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="WMihkXKO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6DAAC207D5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id DF7E480009; Mon, 1 Jun 2020 10:26:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DA7E78E0006; Mon, 1 Jun 2020 10:26:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CBDA980009; Mon, 1 Jun 2020 10:26:51 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0155.hostedemail.com [216.40.44.155]) by kanga.kvack.org (Postfix) with ESMTP id B09848E0006 for ; Mon, 1 Jun 2020 10:26:51 -0400 (EDT) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 6D3F978B32 for ; Mon, 1 Jun 2020 14:26:51 +0000 (UTC) X-FDA: 76880869422.26.shoe65_58e6aa1c10d35 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin26.hostedemail.com (Postfix) with ESMTP id 3FA5B18049DF8 for ; Mon, 1 Jun 2020 14:26:51 +0000 (UTC) X-HE-Tag: shoe65_58e6aa1c10d35 X-Filterd-Recvd-Size: 2621 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf22.hostedemail.com (Postfix) with ESMTP for ; Mon, 1 Jun 2020 14:26:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=qcaW7kM1FeNeZDxjYDiBD+HVABREC6q8IwJJi9uWfas=; b=WMihkXKOcI2hSSU0oFKHkV0u1r Le+5snAEEYV9wkCUV0VMA+ifWaY0vKrtJGErZFhk1nmn4mPayyHGEcF1rgQvQOjrwpJwQt0gy+Zhw 3degdL1kgxN7ESOBhBORSVuMTraNHVDmU47PF9Pw+rQGyPi+qmSKYAb6xYytsDvS56vz+dPR2h3oW 9KUBAdmvnMXdj6UE7/f0yGP9Mcjja6M92/tiG1fHBBH2FkwTvKIbQ0q2e3brpYhKrfnfk61uQ0dIB RqOn0IV+1LLV+NnAdgSPw4WzHumgD+TttCYxuwfiP1K5L3U8MSe/hT7C7FvnGbglsOPRyC4/T8aZ5 cdMRLDng==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jflOr-0003DU-I3; Mon, 01 Jun 2020 14:26:49 +0000 Date: Mon, 1 Jun 2020 07:26:49 -0700 From: Matthew Wilcox To: Jens Axboe Cc: io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org Subject: Re: [PATCH 04/12] mm: add support for async page locking Message-ID: <20200601142649.GJ19604@bombadil.infradead.org> References: <20200526195123.29053-1-axboe@kernel.dk> <20200526195123.29053-5-axboe@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200526195123.29053-5-axboe@kernel.dk> X-Rspamd-Queue-Id: 3FA5B18049DF8 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, May 26, 2020 at 01:51:15PM -0600, Jens Axboe wrote: > +static int __wait_on_page_locked_async(struct page *page, > + struct wait_page_queue *wait, bool set) > +{ > + struct wait_queue_head *q = page_waitqueue(page); > + int ret = 0; > + > + wait->page = page; > + wait->bit_nr = PG_locked; > + > + spin_lock_irq(&q->lock); > + if (set) > + ret = !trylock_page(page); > + else > + ret = PageLocked(page); > + if (ret) { > + __add_wait_queue_entry_tail(q, &wait->wait); > + SetPageWaiters(page); > + if (set) > + ret = !trylock_page(page); > + else > + ret = PageLocked(page); Between the callers and this function, we actually look at PG_lock three times; once in the caller, then after taking the spinlock, then after adding ourselves to the waitqueue. I understand the first and third, but is it really worth doing the second test? It feels unlikely to succeed and only saves us setting PageWaiters.