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AJvYcCWvjSLNwA1BQGyVv9Ed5ijid1fV6Jsxibf3bMl3MndGFCXsoDQrm2fVMIGlhdhVXRhYbNB3Gn23BA==@kvack.org X-Gm-Message-State: AOJu0YzimD7WRx5cURGgiLu0MU9dqBKZDopeRtZaHVM4n0wo1loXFQGA ByluRp311OalqxDkPaN6J4+ydB6m63JVqHIhJ3xsPuu+zGVE5hFMsTmhw+nrhyKEpnpR7gjceKR /BTSvfgTcT0DyHkJo5ZZACN35HJT2hIn3lF2i X-Google-Smtp-Source: AGHT+IFSJBZecszQ20YVP/M3LwFCJvvvxHjk0DXh985IX3HUMPgl7i2cj+lXxs2d3KZP5jUlYop583LH85GYa/xWD7k= X-Received: by 2002:a05:6102:c86:b0:4a4:8928:7181 with SMTP id ada2fe7eead31-4a8cfd69b87mr3199010137.29.1730075131439; Sun, 27 Oct 2024 17:25:31 -0700 (PDT) MIME-Version: 1.0 References: <20241026033625.2237102-1-yuzhao@google.com> <37a28ef7-e477-40b0-a8e4-3d74b747e323@suse.cz> <8459b884-5877-41bd-a882-546e046b9dad@suse.cz> <6ac7a38f-30df-4403-8723-a43829bcdba5@suse.cz> In-Reply-To: <6ac7a38f-30df-4403-8723-a43829bcdba5@suse.cz> From: Yu Zhao Date: Sun, 27 Oct 2024 18:24:54 -0600 Message-ID: Subject: Re: [PATCH mm-unstable v2] mm/page_alloc: keep track of free highatomic To: Vlastimil Babka Cc: Andrew Morton , Johannes Weiner , Zi Yan , Mel Gorman , Matt Fleming , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Link Lin Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 2FDD91A0014 X-Stat-Signature: whjxhr3dschngffp15fhie7seqz4j5e3 X-Rspam-User: X-HE-Tag: 1730075104-338845 X-HE-Meta: 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 D1U/JNFd DwiUdz8Y+IZlAFlfnXy2084Dy4JFc5aKxCQBBjTg9KzSVXq9BP6rgfh+FnIEpxdBQ+8uQzFxM1lIJuU7O/s5ojRQLq7PXnIebtKJQaaiLkGUQasro3BB9gcHvkd3viUpL7UEbwy+PuwZGpy4sbTDVLr+/ruKhXLI230PJBeL/M3z0GMvtmvqBBBiq3CMoAh2EDyhDHqIHuQRTXGkH88oosHxCCj9WGWKDfQaWjXKVdBUuQVo= X-Bogosity: Ham, tests=bogofilter, spamicity=0.030313, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Oct 27, 2024 at 3:05=E2=80=AFPM Vlastimil Babka wr= ote: > > On 10/27/24 21:51, Yu Zhao wrote: > > On Sun, Oct 27, 2024 at 2:36=E2=80=AFPM Vlastimil Babka wrote: > >> > >> On 10/27/24 21:17, Yu Zhao wrote: > >> > On Sun, Oct 27, 2024 at 1:53=E2=80=AFPM Vlastimil Babka wrote: > >> >> > >> > >> For example: > >> > >> - a page is on pcplist in MIGRATE_MOVABLE list > >> - we reserve its pageblock as highatomic, which does nothing to the pa= ge on > >> the pcplist > >> - page above is flushed from pcplist to zone freelist, but it remember= s it > >> was MIGRATE_MOVABLE, merges with another buddy/buddies from the > >> now-highatomic list, the resulting order-X page ends up on the movable > >> freelist despite being in highatomic pageblock. The counter of free > >> highatomic is now wrong wrt the freelist reality > > > > This is the part I don't follow: how is it wrong w.r.t. the freelist > > reality? The new nr_free_highatomic should reflect how many pages are > > exactly on free_list[MIGRATE_HIGHATOMIC], because it's updated > > accordingly. > > You'd have to try implementing your change in the kernel without that > migratetype hygiene series, and see how it would either not work, or you'= d > end up implementing the series as part of that. A proper backport would need to track the MT of the free_list a page is deleted from, and I see no reason why in such a proper backport "the counter could drift easily" or "the counter of free highatomic is now wrong wrt the freelist reality". So I assume you actually mean this patch can't be backported cleanly? (Which I do agree.)