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Tue, 13 Dec 2022 15:53:56 -0800 (PST) X-Google-Smtp-Source: AA0mqf51Jqh+4WEJhTU4iZtLHU49d0jUgx/pvRdiDLO5I6Ppy8t6dKAAJVVlZreokulIGnI/17grT6Iw71IV+auKuMo= X-Received: by 2002:a81:c86:0:b0:3f0:3355:86f2 with SMTP id 128-20020a810c86000000b003f0335586f2mr17786202ywm.88.1670975636731; Tue, 13 Dec 2022 15:53:56 -0800 (PST) MIME-Version: 1.0 References: <20221213234505.173468-1-npache@redhat.com> In-Reply-To: From: Nico Pache Date: Tue, 13 Dec 2022 16:53:30 -0700 Message-ID: Subject: Re: [RFC V2] mm: add the zero case to page[1].compound_nr in set_compound_order To: Mike Kravetz Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, muchun.song@linux.dev, akpm@linux-foundation.org, willy@infradead.org, gerald.schaefer@linux.ibm.com, sidhartha.kumar@oracle.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 66C4518000F X-Stat-Signature: y7eofgy9qxrp6e51sr8pax9g3u1w9pnt X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1670975639-201596 X-HE-Meta: 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 2zCnovxa C7mgF/V1/DCXL1gOT/4m7DSKr++D/PoDuuRjeaPjG7zZNqjTDYV3PGF8fG28mcYfJPpD09z92cMrhzxA= 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: Hi Mike, Thanks for the pointer! Would the branchless conditional be an improvement over the current approach? I'm not sure how hot this path is, but it may be worth the optimization. -- Nico On Tue, Dec 13, 2022 at 4:48 PM Mike Kravetz wrote: > > On 12/13/22 16:45, Nico Pache wrote: > > Since commit 1378a5ee451a ("mm: store compound_nr as well as > > compound_order") the page[1].compound_nr must be explicitly set to 0 if > > calling set_compound_order(page, 0). > > > > This can lead to bugs if the caller of set_compound_order(page, 0) forgets > > to explicitly set compound_nr=0. An example of this is commit ba9c1201beaa > > ("mm/hugetlb: clear compound_nr before freeing gigantic pages") > > There has been some recent work in this area. The latest patch being, > https://lore.kernel.org/linux-mm/20221213212053.106058-1-sidhartha.kumar@oracle.com/ > > -- > Mike Kravetz >