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From: Shakeel Butt To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, kent.overstreet@linux.dev, vbabka@suse.cz, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, usamaarif642@gmail.com, 00107082@163.com, pasha.tatashin@soleen.com, souravpanda@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] alloc_tag: avoid warnings when freeing non-compound "tail" pages Message-ID: References: <20250909233409.1013367-1-surenb@google.com> <20250909233409.1013367-4-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250909233409.1013367-4-surenb@google.com> X-Migadu-Flow: FLOW_OUT X-Stat-Signature: zqhr96a76o7dgy4kxsjpgpxkcewfmyoo X-Rspam-User: X-Rspamd-Queue-Id: BF862100012 X-Rspamd-Server: rspam10 X-HE-Tag: 1757620888-283340 X-HE-Meta: U2FsdGVkX190CBjBeUbXAv2q9SThQgLpDmbGgo/Z85h3zTSG3oLLxEMMoj8LBQ2PyeZzLhzaHgWcJmSdFROfb6fu9vbmn9LAMN6XiYDJTw2z7+dAVpeFCZkr1vadPgkc79SuTbvKFPEbT9ZwaDYPtkhMrrOPcOpI0wZy1A++YKQYc7WXIyyzXxuWKsQ2UOKymMPSTAhpq4a5gFuQXzW3GbLosxwBVRUUvm4lG/dy3cydUsKcpDYjggvM86Dh95WE7a1anCL7PciuWnbwo4mAANhmq/4fVTsfQCmaeLBPSnrMgBqxzKYosIBlZ0tleNgrjG+AqHtflheljjXli4MPJrQNKTHtfsEQswDBCx+gNtOCm2Fkkdz07PcPTxHfm4o94mpvE9tWoYwavxmHP1XotSuEYkWQw0pknyd7mLsrmP4B1oYzDV4D+EUABZtgZltBK27edfYBPB2EMbdi6+R6gx11FY30rGK8QejHj1sP7SmhnmAOSwAw0fNIoyP+n7WrWny3CEC46hoc6h1H5X4AlE3KD0nQw+JZAKEbcoENMlxPY+r24OQt4WOn/W91ntKPTbA4TAa3cr995iv1UUcydPg5iGV+kinXFMJyvytE85g/bFNqpaBKbdo9pzrIdaBHyhKnLUksDtBg8fsMFNskhLDjZnyoC5Mux0OQaKVU3r9K5eUs7QSdxpZwsWIUuqmiJy9zuaOxapHoAV911hvbeKlpi3mFOLQ/4dolYa1TcPNagfB6iTxINxzJBNAbStPGVb1W/0+9yTOoGwXLLV45fQf0N+GY9LIiMj0HzSK4UX/8yQYBIpd7GEIBMAUKoIgjKz5ju8/RDMDjJMEjh+tylMnaft7thUhGxvJalgqfJaufTvIRI47YGJcuGRGHcX5Udj7sJOeiLaEw7g8eglOy1bhazAM796mW/wY3RqwTDfvhcKHhiQKUPkkN9x1knm/w0A1/7s4y+sP09RdPDZ5 0V84Lp4O MZw77iffN2jfwCSFELdrkI+XexoQ+GXhiknmnYeKXHfOimUK38bZRtA0n41cdhOc43HMQ7X+w2E01Wo2Km/luaNvJYkv+pE/Qd5R/QWSSHcdzCH8v0wg+fMxJa2zCbRcmArgtRqpnEDdaxUPVeWfWUb6CExemxkWynlwu9weYjk7pxK6/vWezz8MSjyRZGTm68LDgjQwctEHkUbyv07E912LAWdZMdbuhR8Ew8xbGn7QcwMfvQE14CIjmrEQBDLiDP8qoMOr/83kLBnD+eGYrl9cOQXakjXr8pItBS0KqPnO7pP7s3JvPoDUEzgJYi0aKplu7UmmZhyEXl1Q= 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: List-Subscribe: List-Unsubscribe: On Tue, Sep 09, 2025 at 04:34:09PM -0700, Suren Baghdasaryan wrote: > When freeing "tail" pages of a non-compount high-order page, we properly > subtract the allocation tag counters, however later when these pages are > released, alloc_tag_sub() will issue warnings because tags for these pages > are NULL. > This issue was originally anticipated by Vlastimil in his review [1] and > then recently reported by David. > Prevent warnings by marking the tags empty. > > [1] https://lore.kernel.org/all/6db0f0c8-81cb-4d04-9560-ba73d63db4b8@suse.cz/ > > Suggested-by: David Wang <00107082@163.com> > Signed-off-by: Suren Baghdasaryan > --- > mm/page_alloc.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 1760346bbd24..d21a411e807e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5240,9 +5240,16 @@ static void ___free_pages(struct page *page, unsigned int order, > __free_frozen_pages(page, order, fpi_flags); > else if (!head) { > pgalloc_tag_sub_pages(tag, (1 << order) - 1); > - while (order-- > 0) > + while (order-- > 0) { > + /* > + * The "tail" pages of this non-compound high-order > + * page will have no code tags, so to avoid warnings > + * mark them as empty. > + */ > + clear_page_tag_ref(page + (1 << order)); Do we need something similar for the release_pages() code path or is it happening already? > __free_frozen_pages(page + (1 << order), order, > fpi_flags); > + } > } > } > > -- > 2.51.0.384.g4c02a37b29-goog >