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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id g64sm5273422qke.43.2019.12.05.15.58.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Dec 2019 15:58:21 -0800 (PST) Content-Type: text/plain; charset=utf-8 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 18:58:20 -0500 Message-Id: <2139CED9-6C12-48A5-BF61-F36923EB948E@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=0.145405, 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 6:24 PM, John Hubbard wrote: >=20 > Let's check in the fix that is clearly correct and non-controversial, in o= ne > patch. Then another patch can be created for the other case. This allows f= orward > progress and quick resolution of the user's bug report, while still dealin= g > with all the problems. >=20 > If you try to fix too many problems in one patch (and remember, sometimes "= >1" > is too many), then things bog down. It's always a judgment call, but what'= s=20 > unfolding here is quite consistent with the usual judgment calls in this a= rea. >=20 > I don't think anyone is saying, "don't work on the second problem", it's j= ust > that it's less urgent, due to no reports from the field. If you are passio= nate > about fixing the second problem (and are ready and willing to handle the f= allout > from user space, if it occurs), then I'd encourage you to look into it. >=20 > It could turn out to be one of those "cannot change this because user spac= e expectations > have baked and hardened, and changes would break user space" situations, j= ust to > warn you in advance, though. There is no need to paper over the underlying issue. One can think there is o= nly one problem. The way move_pages() deal with pages are already in the des= ired node. Then, I don=E2=80=99t see there is any controversy that it was br= oken for so long and just restore it to according to the manpage. If you wor= ried about people has already depended on the broken behavior, it could stay= in linux-next for many releases to gather feedback. In any case, I don=E2=80= =99t see it need to hurry to fix this until someone can show the real world u= se case for it apart from some random test code.=