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b=f4biDeBJ6tcql1AACsjQmcSyt2 d83oKifGra+ytLN2uZfmePX0tbVE6dnKn1WfJ3OvlN9URdjn9F1hJOrwg4FIu8Uwm52dJliu/zpQ9 h96QZ4hXbuvGHfI2Fv60NbBkIpm6lgfFqEqCOSPxp7QvANPdUBrt4P0JYQw2Q42hHtIWuEtgGqbPo 0+gUcp3OGJMz2AbREPzjIOVaiIFq6ni7gsazZOuPivrdYAz7fLawDuFGA6KyncJ1L+0x9/sTFe/iM B2FMi50IIQnWC0ciz9Htfa0cG0ugjRQYV2/PKFRgxjXmVZ7zFYdIVS9XKJyN0Mm/DjYn4NIg12POx f9lWqbww==; Received: from fangorn.home.surriel.com ([10.0.13.7]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1vOHCb-000000000s9-23S9; Wed, 26 Nov 2025 10:13:06 -0500 Message-ID: <177c8e4d0567456baecc962bf5c1038f05358cc0.camel@surriel.com> Subject: Re: [PATCH v12 mm-new 06/10] mm: bpf-thp: add support for global mode From: Rik van Riel To: Alexei Starovoitov , Yafang Shao Cc: Andrew Morton , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , David Hildenbrand , Lorenzo Stoakes , Martin KaFai Lau , Eduard , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Zi Yan , Liam Howlett , npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, Johannes Weiner , usamaarif642@gmail.com, gutierrez.asier@huawei-partners.com, Matthew Wilcox , Amery Hung , David Rientjes , Jonathan Corbet , Barry Song <21cnbao@gmail.com>, Shakeel Butt , Tejun Heo , lance.yang@linux.dev, Randy Dunlap , Chris Mason , bpf , linux-mm Date: Wed, 26 Nov 2025 10:13:06 -0500 In-Reply-To: References: <20251026100159.6103-1-laoar.shao@gmail.com> <20251026100159.6103-7-laoar.shao@gmail.com> Autocrypt: addr=riel@surriel.com; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.3 (3.54.3-2.fc41) MIME-Version: 1.0 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 6CF4C8001A X-Stat-Signature: hydfxr3otsqwxigort6wpwb41y8ytf4s X-Rspam-User: X-HE-Tag: 1764170448-351338 X-HE-Meta: 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 yXt6jmmI JHyiz1hvrl7UHPotZlCQaQJ+GTu8awzOcVWAILBzBthQYmIXnu9eln8DYotoqRY/2xlhzCDF5y3JXOcaeMuFL06BGPth+HdSO55Gb09UIxHlY3tFS2wJm/HfmXn7ZDxH0hvqWS1f3RyZQn2qhx+AysX/ehr/RKxBePfFKORNQ6ZNhWtN7d5gpRGJSFKWY2zGhjfhgH1kZT4yBpxhNpIW/KpJuxmWmqMD2aqFUYURhJVVhoUp5ze5k5qsPs/42mzdRjnEgAoaD61e/McRA4rwWERz4EbfCaxNLOJrx3NmlQ1lQsNhi10v8Qe0z3bySULW/0mIN 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, 2025-10-28 at 18:32 -0700, Alexei Starovoitov wrote: > On Sun, Oct 26, 2025 at 3:03=E2=80=AFAM Yafang Shao > wrote: > >=20 > > The per-process BPF-THP mode is unsuitable for managing shared > > resources > > such as shmem THP and file-backed THP. This aligns with known > > cgroup > > limitations for similar scenarios [0]. > >=20 > > Introduce a global BPF-THP mode to address this gap. When > > registered: > > - All existing per-process instances are disabled > > - New per-process registrations are blocked > > - Existing per-process instances remain registered (no forced > > unregistration) > >=20 > > The global mode takes precedence over per-process instances. > > Updates are > > type-isolated: global instances can only be updated by new global > > instances, and per-process instances by new per-process instances. >=20 > ... >=20 > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 spin_lock(&thp_ops_lock); > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Each process is exclusively ma= naged by a single BPF-THP. > > */ > > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (rcu_access_pointer(mm->bpf_mm= .bpf_thp)) { > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Each process is exclusively ma= naged by a single BPF-THP. > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * Global mode disables per-= process instances. > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */ > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (rcu_access_pointer(mm->bpf_mm= .bpf_thp) || > > rcu_access_pointer(bpf_thp_global)) { > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 err =3D -EBUSY; > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 goto out; > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >=20 > You didn't address the issue and instead doubled down > on this broken global approach. >=20 > This bait-and-switch patchset is frankly disingenuous. > 'lets code up some per-mm hack, since people will hate it anyway, > and I'm not going to use it either, and add this global mode > as a fake "fallback"...' Should things be the other way around, where per-process BPF THP policy overrides global policy? I can definitely see a use for global policy, but also a reason to override it for some programs or containers. --=20 All Rights Reversed.