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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 74AE7C4332F for ; Tue, 18 Oct 2022 18:02:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230152AbiJRSB5 (ORCPT ); Tue, 18 Oct 2022 14:01:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56728 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230149AbiJRSBs (ORCPT ); Tue, 18 Oct 2022 14:01:48 -0400 Received: from mail-pj1-x1033.google.com (mail-pj1-x1033.google.com [IPv6:2607:f8b0:4864:20::1033]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8B2A61147; Tue, 18 Oct 2022 11:01:44 -0700 (PDT) Received: by mail-pj1-x1033.google.com with SMTP id o17-20020a17090aac1100b0020d98b0c0f4so16750712pjq.4; Tue, 18 Oct 2022 11:01:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=kbVWeBLmoXaL5wT4FGVpRcLjWyd0m50VYE8PAOnnEko=; b=a0iG9+gDGzV0/uFEh+xecDTUMLAjs0avyQ2SwEVTlqQ0OWuxIWVvI7+VGzewqEagT7 5N1mcJO41KbKS7i/17ZW9QV3RoHCd4fgRihwlp6D5/+M0mqFYNoJYrou3tjrqrlTJ8dz XbKOlmlgCSm7t4iqfFRIJOMlef9tuCJ85wiUwPbLRtSwyRA1hArJi9oGz7TdQwhuEumS xDaJQz404PU7P6NsWFLsZENDAml1aJHAJ3OBdTrq6GH4hjxTkfT6Qmn14UOcrFVPZstD 4oqbVikV/Ib0yqaGyN6ev3o2wWLK/uUDQCFdWKkr6BcCUVKSR7lOgRAYhE4EsX7u7G0i 93qQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=kbVWeBLmoXaL5wT4FGVpRcLjWyd0m50VYE8PAOnnEko=; b=jKMmG5SrEkiTJQMxBJyt6TocG9csYlZaDf1pGLMVcGkN26fVYXgzg6YYPR5+/JtDBk uAiLUABbZElx8UTI+51oUPMha66toqE4yP2RHZ1aATmObpMekhYDOf0E2mPG89a3OqH7 qJIYfVW7luFimjWIUgQfCHfFy3IJzD11oO1YZbEdurRN/+pZJIh1Q9IDmqaPtb5GNSkE 5y0LZ+JsqrirgpyqGl7LEUnQZ+3LPh1Jk8w+6EwPAmJYF1hWoi7AU4dYzdnLZ5DVKht+ pQO6TromTBLQalyuE2j+C+lTsX/iS2LiR09zB2V8WKl+/T25DNcoqS9GOFbuu4YA+JAf qfsw== X-Gm-Message-State: ACrzQf08iiew1kLNqo5RotvAEJSCq5crV4WIp1nWXGSOt0UeLFH7Zozg moWryXEgdIOkcKdRBtOQ5lyAz1hVquGHfXIvt9I= X-Google-Smtp-Source: AMsMyM4dRCMlLxwxpvWPKeEBQqgqTpkBvzI2y4UmcFNFY7lhRcumit+v8Ysop8DlhVkW1Pg4yIXBLJ/OEQVZxMId9tQ= X-Received: by 2002:a17:902:d512:b0:181:f1f4:fcb4 with SMTP id b18-20020a170902d51200b00181f1f4fcb4mr4248525plg.102.1666116103439; Tue, 18 Oct 2022 11:01:43 -0700 (PDT) MIME-Version: 1.0 References: <20221005180341.1738796-1-shy828301@gmail.com> <20221005180341.1738796-3-shy828301@gmail.com> <20221013123830.opbulq4qad56kuev@techsingularity.net> <20221017094132.vnanndrwa2yn7qcw@techsingularity.net> In-Reply-To: <20221017094132.vnanndrwa2yn7qcw@techsingularity.net> From: Yang Shi Date: Tue, 18 Oct 2022 11:01:31 -0700 Message-ID: Subject: Re: [PATCH 2/4] mm: mempool: introduce page bulk allocator To: Mel Gorman Cc: agk@redhat.com, snitzer@kernel.org, dm-devel@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 17, 2022 at 2:41 AM Mel Gorman wrote: > > On Thu, Oct 13, 2022 at 01:16:31PM -0700, Yang Shi wrote: > > On Thu, Oct 13, 2022 at 5:38 AM Mel Gorman wrote: > > > > > > On Wed, Oct 05, 2022 at 11:03:39AM -0700, Yang Shi wrote: > > > > Since v5.13 the page bulk allocator was introduced to allocate order-0 > > > > pages in bulk. There are a few mempool allocator callers which does > > > > order-0 page allocation in a loop, for example, dm-crypt, f2fs compress, > > > > etc. A mempool page bulk allocator seems useful. So introduce the > > > > mempool page bulk allocator. > > > > > > > > It introduces the below APIs: > > > > - mempool_init_pages_bulk() > > > > - mempool_create_pages_bulk() > > > > They initialize the mempool for page bulk allocator. The pool is filled > > > > by alloc_page() in a loop. > > > > > > > > - mempool_alloc_pages_bulk_list() > > > > - mempool_alloc_pages_bulk_array() > > > > They do bulk allocation from mempool. > > > > They do the below conceptually: > > > > 1. Call bulk page allocator > > > > 2. If the allocation is fulfilled then return otherwise try to > > > > allocate the remaining pages from the mempool > > > > 3. If it is fulfilled then return otherwise retry from #1 with sleepable > > > > gfp > > > > 4. If it is still failed, sleep for a while to wait for the mempool is > > > > refilled, then retry from #1 > > > > The populated pages will stay on the list or array until the callers > > > > consume them or free them. > > > > Since mempool allocator is guaranteed to success in the sleepable context, > > > > so the two APIs return true for success or false for fail. It is the > > > > caller's responsibility to handle failure case (partial allocation), just > > > > like the page bulk allocator. > > > > > > > > The mempool typically is an object agnostic allocator, but bulk allocation > > > > is only supported by pages, so the mempool bulk allocator is for page > > > > allocation only as well. > > > > > > > > Signed-off-by: Yang Shi > > > > > > Overall, I think it's an ok approach and certainly a good use case for > > > the bulk allocator. > > > > > > The main concern that I have is that the dm-crypt use case doesn't really > > > want to use lists as such and it's just a means for collecting pages to pass > > > to bio_add_page(). bio_add_page() is working with arrays but you cannot > > > use that array directly as any change to how that array is populated will > > > then explode. Unfortunately, what you have is adding pages to a list to > > > take them off the list and put them in an array and that is inefficient. > > > > Yeah, I didn't think of a better way to pass the pages to dm-crypt. > > > > > > > > How about this > > > > > > 1. Add a callback to __alloc_pages_bulk() that takes a page as a > > > parameter like bulk_add_page() or whatever. > > > > > > 2. For page_list == NULL && page_array == NULL, the callback is used > > > > > > 3. Add alloc_pages_bulk_cb() that passes in the name of a callback > > > function > > > > > > 4. In the dm-crypt case, use the callback to pass the page to bio_add_page > > > for the new page allocated. > > > > Thank you so much for the suggestion. But I have a hard time > > understanding how these work together. Do you mean call bio_add_page() > > in the callback? But bio_add_page() needs other parameters. Or I > > misunderstood you? > > > > I expected dm-crypt to define the callback. Using bio_add_page > directly would not work as the bulk allocator has no idea what to pass > bio_add_page. dm-crypt would likely need to create both a callback and an > opaque data structure passed as (void *) to track "clone" and "len" I see. Yeah, we have to pass the "clone" and "len" to the callback via pool_data. It should not be hard since dm-crypt already uses crypt_config to maintain a counter for allocated pages, we should just need to pass the struct to the callback as a parameter. But I'm wondering whether this is worth it or not? Will it make the code harder to follow? > > -- > Mel Gorman > SUSE Labs