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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 18BFCC4332F for ; Mon, 17 Oct 2022 09:41:39 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 388766B0072; Mon, 17 Oct 2022 05:41:38 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 338BC6B0074; Mon, 17 Oct 2022 05:41:38 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 201746B0075; Mon, 17 Oct 2022 05:41:38 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 0C4196B0072 for ; Mon, 17 Oct 2022 05:41:38 -0400 (EDT) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id BA67540D20 for ; Mon, 17 Oct 2022 09:41:37 +0000 (UTC) X-FDA: 80029949034.05.AB8EC58 Received: from outbound-smtp18.blacknight.com (outbound-smtp18.blacknight.com [46.22.139.245]) by imf29.hostedemail.com (Postfix) with ESMTP id 25C3512003A for ; Mon, 17 Oct 2022 09:41:35 +0000 (UTC) Received: from mail.blacknight.com (pemlinmail01.blacknight.ie [81.17.254.10]) by outbound-smtp18.blacknight.com (Postfix) with ESMTPS id 5FADD1C3C0F for ; Mon, 17 Oct 2022 10:41:34 +0100 (IST) Received: (qmail 4063 invoked from network); 17 Oct 2022 09:41:34 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.198.246]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 17 Oct 2022 09:41:34 -0000 Date: Mon, 17 Oct 2022 10:41:32 +0100 From: Mel Gorman To: Yang Shi 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 Subject: Re: [PATCH 2/4] mm: mempool: introduce page bulk allocator Message-ID: <20221017094132.vnanndrwa2yn7qcw@techsingularity.net> References: <20221005180341.1738796-1-shy828301@gmail.com> <20221005180341.1738796-3-shy828301@gmail.com> <20221013123830.opbulq4qad56kuev@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1665999696; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=S13sFuTHswn9t8UWriob3QGuAvRLSQnyQGcFlgz2RJ4=; b=rIrw73jphV1mB+ZbZQHLqs+t7ipDYnMv3wuqPOOiNilG/PjJnrQEUnIMSPuxXrNKdwLzN4 5vvQSSlnfGa9Uf6Jt6A7bo3XtecoAuAV8neVlapR0V+TZDZKiw/+QthvQS7W76wfYtFA8I TLLGFlf+UtClnvjZEF6AKoTxTPc0s/Q= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=none; spf=pass (imf29.hostedemail.com: domain of mgorman@techsingularity.net designates 46.22.139.245 as permitted sender) smtp.mailfrom=mgorman@techsingularity.net; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1665999696; a=rsa-sha256; cv=none; b=n+H9ZnsTU9z+cPwRccJo1/68JNo/Tfjekpvyrjuisd+k5IzX9eAFPWph+EWlU/AOqxGmS2 7K/rFfjDPTbfPtWlxkcr3wOlmmoLhxL9EXnAGQDFO86yDeT2xghD3Yk7hCUJ4lu/J8JymS 7S7Mi3N+x2GQ0z4f0GV+2Y0BQxDu7v8= X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 25C3512003A X-Rspam-User: Authentication-Results: imf29.hostedemail.com; dkim=none; spf=pass (imf29.hostedemail.com: domain of mgorman@techsingularity.net designates 46.22.139.245 as permitted sender) smtp.mailfrom=mgorman@techsingularity.net; dmarc=none X-Stat-Signature: 4zqmbqmgonir8drp4iif8tom59qwodzj X-HE-Tag: 1665999695-108181 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: 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" -- Mel Gorman SUSE Labs