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=-12.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 2BB42C4346E for ; Tue, 22 Sep 2020 02:02:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F021D23A75 for ; Tue, 22 Sep 2020 02:02:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729420AbgIVCCI (ORCPT ); Mon, 21 Sep 2020 22:02:08 -0400 Received: from shelob.surriel.com ([96.67.55.147]:45670 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729366AbgIVCCE (ORCPT ); Mon, 21 Sep 2020 22:02:04 -0400 Received: from imladris.surriel.com ([96.67.55.152]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94) (envelope-from ) id 1kKXcv-0003Cm-EZ; Mon, 21 Sep 2020 22:01:53 -0400 From: Rik van Riel To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, kernel-team@fb.com, niketa@fb.com, akpm@linux-foundation.org, sjenning@redhat.com, ddstreet@ieee.org, konrad.wilk@oracle.com, hannes@cmpxchg.org, Rik van Riel Subject: [PATCH 2/2] mm,swap: skip swap readahead if page was obtained instantaneously Date: Mon, 21 Sep 2020 22:01:48 -0400 Message-Id: <20200922020148.3261797-3-riel@surriel.com> X-Mailer: git-send-email 2.25.4 In-Reply-To: <20200922020148.3261797-1-riel@surriel.com> References: <20200922020148.3261797-1-riel@surriel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: riel@shelob.surriel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Check whether a swap page was obtained instantaneously, for example because it is in zswap, or on a very fast IO device which uses busy waiting, and we did not wait on IO to swap in this page. If no IO was needed to get the swap page we want, kicking off readahead on surrounding swap pages is likely to be counterproductive, because the extra loads will cause additional latency, use up extra memory, and chances are the surrounding pages in swap are just as fast to load as this one, making readahead pointless. Signed-off-by: Rik van Riel --- mm/swap_state.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/mm/swap_state.c b/mm/swap_state.c index aacb9ba53f63..6919f9d5fe88 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -637,6 +637,7 @@ static struct page *swap_cluster_read_one(swp_entry_t entry, struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, struct vm_fault *vmf) { + struct page *page; unsigned long entry_offset = swp_offset(entry); unsigned long offset = entry_offset; unsigned long start_offset, end_offset; @@ -668,11 +669,18 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, end_offset = si->max - 1; blk_start_plug(&plug); + /* If we read the page without waiting on IO, skip readahead. */ + page = swap_cluster_read_one(entry, offset, gfp_mask, vma, addr, false); + if (page && PageUptodate(page)) + goto skip_unplug; + + /* Ok, do the async read-ahead now. */ for (offset = start_offset; offset <= end_offset ; offset++) { - /* Ok, do the async read-ahead now */ - swap_cluster_read_one(entry, offset, gfp_mask, vma, addr, - offset != entry_offset); + if (offset == entry_offset) + continue; + swap_cluster_read_one(entry, offset, gfp_mask, vma, addr, true); } +skip_unplug: blk_finish_plug(&plug); lru_add_drain(); /* Push any new pages onto the LRU now */ -- 2.25.4