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 C64F7C433F5 for ; Fri, 18 Mar 2022 08:41:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233902AbiCRImV (ORCPT ); Fri, 18 Mar 2022 04:42:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33298 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233893AbiCRImI (ORCPT ); Fri, 18 Mar 2022 04:42:08 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 14C4817869D for ; Fri, 18 Mar 2022 01:40:49 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 6A5CEB82196 for ; Fri, 18 Mar 2022 08:40:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4AF8BC340EC; Fri, 18 Mar 2022 08:40:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1647592846; bh=xJBQDlqFBXax04cp7hOQvnVKZ6NiGsFEY3WOnqxW2E8=; h=From:To:Cc:Subject:Date:In-Reply-To:From; b=LMs11+rR98X2oRKX9OnwUUF04p026YBDauZ9lqxwN8foHG+6lAUQ6tDRZsgmPz7k4 cpyU5sMzVa9l1X18tSDdebc9SlXxMuXIcXCZ2CtEIWDqsnOBCKBVVO7AZVDGfysV6N GMI8i2UbUwih6X5PAgfyGKkOr5DVcR+98V+5yhUylH4Jz3RrGo1QhTyYtJsqQj4whP ngPJ5uZ5nY1ZMYVlBEqHsilJnez+FhdZ1efBXWyAVfEvNgPur04HpIpRt3l1ZWKka8 ALLYPIT2g+cB9xO4BQwoG67SHeT7dye5I8kv5FeRn5JL4bwaR8Q9MkUhikG79DHXsT 8E82IY7A9ixNg== From: sj@kernel.org To: David Hildenbrand Cc: xhao@linux.alibaba.com, sj@kernel.org, rongwei.wang@linux.alibaba.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Baolin Wang Subject: Re: [RFC PATCH V1 0/3] mm/damon: Add CMA minotor support Date: Fri, 18 Mar 2022 08:40:41 +0000 Message-Id: <20220318084041.25949-1-sj@kernel.org> X-Mailer: git-send-email 2.17.1 MIME-Version: 1.0 In-Reply-To: <5c46548a-04b9-607e-f43a-63545131d336@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 18 Mar 2022 09:29:20 +0100 David Hildenbrand wrote: > On 18.03.22 06:13, xhao@linux.alibaba.com wrote: > > > > On 3/18/22 12:42 AM, David Hildenbrand wrote: > >> On 17.03.22 08:03, Xin Hao wrote: > >>> Hi David, > >>> > >>> On 3/16/22 11:09 PM, David Hildenbrand wrote: > >>>> On 15.03.22 17:37, Xin Hao wrote: > >>>> > >>>> s/minotor/monitor/ > >>> Thanks, i will fix it. > >>>>> The purpose of these patches is to add CMA memory monitoring function. > >>>>> In some memory tight scenarios, it will be a good choice to release more > >>>>> memory by monitoring the CMA memory. > >>>> I'm sorry, but it's hard to figure out what the target use case should > >>>> be. Who will release CMA memory and how? Who will monitor that? What are > >>>> the "some memory tight scenarios"? What's the overall design goal? > >>> I may not be describing exactly what i mean，My intention is to find out > >>> how much of the reserved CMA space is actually used and which is unused, > >>> For those that are not used, I understand that they can be released by > >>> cma_release(). Of course, This is just a little personal thought that I > >>> think is helpful for saving memory. > >> Hm, not quite. We can place movable allocations on cma areas, to be > >> migrated away once required for allocations via CMA. So just looking at > >> the pages allocated within a CMA area doesn't really tell you what's > >> actually going on. > > > > I don't think so, the damon not looking at the pages allocate, It is > > constantly monitoring who is using CMA area pages through tracking page > > access bit > > > > in the kernel via the kdamond.x thread, So through damon, it can tell us > > about the hot and cold distribution of CMA memory. > > I'm not sure I follow. With random movable pages being placed on the CMA > area, the mentioned use case of "cma_release()" to release pages doesn't > make sense to me. > > I assume I'm missing the big picture -- and that should be properly > documented in the patch description. We don't add stuff just because it > could be used somehow, there should be a clear motivation how it can > actually be used. Same opinion from my side. The purpose and usage of this patch is unclear to me. Could you please clarify more, Xin? Thanks, SJ > > -- > Thanks, > > David / dhildenb