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Thu, 05 Oct 2023 21:00:36 -0700 (PDT) MIME-Version: 1.0 References: <20231004153248.3842997-1-fvdl@google.com> <20231006003826.GA251100@monkey> In-Reply-To: <20231006003826.GA251100@monkey> From: Frank van der Linden Date: Thu, 5 Oct 2023 21:00:25 -0700 Message-ID: Subject: Re: [PATCH] mm, hugetlb: remove HUGETLB_CGROUP_MIN_ORDER To: Mike Kravetz Cc: linux-mm@kvack.org, muchun.song@linux.dev, akpm@linux-foundation.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: y8ryf9eafcehmnydarrmd4qe1fir3oxn X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 8645B1A0021 X-HE-Tag: 1696564837-25630 X-HE-Meta: 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 DNWjHne2 nfONmHPlzUGM0lb0G4z8aOqY1zrDslbwen1f8fGjm3jg3qwFg0d+eQLNNw9y7idpux2xa6CqvTaBHx6vyOGfAHa/CqJZ2denPyjnIIQ20gseejP9keRTNFSKVjTduofzmLPLL++4TZt/jq3W6/Fe/gkMxrfLEtMQIZLiL317Sp+yldM7DA0owf/angHIOYkjTW/04UcES8PVtmFobuzxJ3BkAHpYX1Ck2nElVO4nx65sx//aiEQh4CSEo+man0+kE9fY894zThbWbSWJ//BPsqPx+BJsgG/MsdRN8Ltav5n1izRc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.031427, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Oct 5, 2023 at 5:53=E2=80=AFPM Mike Kravetz wrote: > > On 10/04/23 15:32, Frank van der Linden wrote: > > Originally, hugetlb_cgroup was the only hugetlb user of tail page > > structure fields. So, the code defined and checked against > > HUGETLB_CGROUP_MIN_ORDER to make sure pages weren't too small > > to use. > > > > However, by now, tail page #2 is used to store hugetlb > > hwpoison and subpool information as well. In other words, > > without that tail page hugetlb doesn't work. > > When I first read this, I thought we might be exposed today. But, I see > that currently order must be > 0 so we are covered. > > > Acknowledge this fact by getting rid of HUGETLB_CGROUP_MIN_ORDER > > and checks against it. Instead, just check for the minimum viable > > page order at hstate creation time. > > IIUC, we do lose the ability to run with an order 1 hstate. Correct? > The minimum must now be 2. > I do not think is worth worrying about. And, the code checking for the > VERY unlikely case where order could be big enough to to be valid, but > too small for cgroups was strange. Theoretically, order 1 hstate (without hugetlb cgroup) used to be possible, since the subpool pointer was in the 1st tail page. But dad6a5eb55 ("mm,hugetlb: use folio fields in second tail page") moved everything to fields in the 2nd tail page, so that hasn't worked for a bit. I guess it would have let you create it, but things would have gone south pretty quickly.. > > > I think this is a nice simplification. Thanks for the review, - Frank