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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id j12sm5343442qkk.36.2019.12.05.15.16.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Dec 2019 15:16:59 -0800 (PST) Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable From: Qian Cai Mime-Version: 1.0 (1.0) Subject: Re: [v3 PATCH] mm: move_pages: return valid node id in status if the page is already on the target node Date: Thu, 5 Dec 2019 18:16:58 -0500 Message-Id: <4C589824-CA40-41A3-8F2B-C2AA2A924510@lca.pw> References: Cc: Yang Shi , fabecassis@nvidia.com, mhocko@suse.com, cl@linux.com, vbabka@suse.cz, mgorman@techsingularity.net, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org In-Reply-To: To: John Hubbard X-Mailer: iPhone Mail (17B111) X-Bogosity: Ham, tests=bogofilter, spamicity=0.122677, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > On Dec 5, 2019, at 5:41 PM, John Hubbard wrote: >=20 > Please recall how this started: it was due to a report from a real end use= r, who was=20 > seeing a real problem. After a few emails, it was clear that there's not a= good > work around available for cases like this: >=20 > * User space calls move_pages(), gets 0 (success) returned, and based on t= hat, > proceeds to iterate through the status array. >=20 > * The status array remains untouched by the move_pages() call, so confusio= n and > wrong behavior ensues. >=20 > After some further discussion, we decided that the current behavior really= is=20 > incorrect, and that it needs fixing in the kernel. Which this patch does. Well, that test code itself does not really tell any real world use case. A= lso, thanks to the discussion, it brought to me it is more obvious and criti= cal that the return code is wrong according to the spec. Then, if that part= is taking care of, it would kill two-bird with one stone because there is n= o need to return status array anymore. Make sense?=