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AJvYcCXWOm6glbMKO651nqfdS4LsVOyRiaVYX8l+7G4DsLlTbeUAD+sgtP9yI1gxJ04xQirdeadPjKDusg==@kvack.org X-Gm-Message-State: AOJu0YztldmLzW7lmh1Wp0FNDjsP2izhkR230XR2E3DDm7wf7RI0XzI4 OYUL4UCkkw5ov3yuaWrowYgJPg1unFW60izleqpqHaUpLa0VX3js8xrHRGM+b/Sjgkvt3lnKGMq Wx6YujqE4KUCol5vINC+WkYjfTXNlXbo= X-Gm-Gg: ASbGnct+0EkG22BIN6dzbRdeRKwsn2F8+PvRI24r5NcCj0VlOKoJdq9mgbyj73FYq1d QtMHCNanLo7DcfngcEeKjDISJX3jn/V9Vz9hu6igxdubvgVkRMr4sOEvCKecAEwYIYT9BE2pwHG fA3NeFVtY7YsANkfbDcop3nGWeuj4y6uOFBy2+DMKHp/CH9NsCtKe+0M8wq8us2AyFZqgF4g7i6 w31r9Ud132JtbunVuFFfreK3d4L1cxaDfOYm0QOkYQE1akZIEXewSsRW+efoJJak9yqnjFV X-Google-Smtp-Source: AGHT+IGAN6hw0WwRvKtq3B1y0SiTrVIZoYnrx0iULGRASJtLgN5JvkICVwdenSNU90hNH8FkNZBvjoCAptWUticznOo= X-Received: by 2002:a05:690c:6289:b0:76c:b76c:ddaf with SMTP id 00721157ae682-78628e24788mr15670597b3.5.1761704053447; Tue, 28 Oct 2025 19:14:13 -0700 (PDT) MIME-Version: 1.0 References: <20251026100159.6103-1-laoar.shao@gmail.com> <20251026100159.6103-7-laoar.shao@gmail.com> In-Reply-To: From: Yafang Shao Date: Wed, 29 Oct 2025 10:13:37 +0800 X-Gm-Features: AWmQ_bl6ri9Brpc7kQ08rlFDC7Zg4B3FVd1R7XVe5An1qRSKX_V24AXUbVkKMWI Message-ID: Subject: Re: [PATCH v12 mm-new 06/10] mm: bpf-thp: add support for global mode To: Alexei Starovoitov 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam05 X-Stat-Signature: qu5f7drrgp5mxqrcea5sbamwwwjoo816 X-Rspam-User: X-Rspamd-Queue-Id: 7540A80004 X-HE-Tag: 1761704054-230883 X-HE-Meta: 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 V+qJDNOz 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 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 Wed, Oct 29, 2025 at 9:33=E2=80=AFAM Alexei Starovoitov wrote: > > On Sun, Oct 26, 2025 at 3:03=E2=80=AFAM Yafang Shao wrote: > > > > The per-process BPF-THP mode is unsuitable for managing shared resource= s > > such as shmem THP and file-backed THP. This aligns with known cgroup > > limitations for similar scenarios [0]. > > > > 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 unregistr= ation) > > > > The global mode takes precedence over per-process instances. Updates ar= e > > type-isolated: global instances can only be updated by new global > > instances, and per-process instances by new per-process instances. > > ... > > > spin_lock(&thp_ops_lock); > > - /* Each process is exclusively managed by a single BPF-THP. */ > > - if (rcu_access_pointer(mm->bpf_mm.bpf_thp)) { > > + /* Each process is exclusively managed by a single BPF-THP. > > + * Global mode disables per-process instances. > > + */ > > + if (rcu_access_pointer(mm->bpf_mm.bpf_thp) || rcu_access_pointe= r(bpf_thp_global)) { > > err =3D -EBUSY; > > goto out; > > } > > You didn't address the issue and instead doubled down > on this broken global approach. > > 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"...' > > The way the previous thread evolved and this followup hack > I don't see a genuine desire to find a solution. > Just relentless push for global mode. > > Nacked-by: Alexei Starovoitov > > Please carry it in all future patches. To move forward, I'm happy to set the global mode aside for now and potentially drop it in the next version. I'd really like to hear your perspective on the per-process mode. Does this implementation meet your needs? -- Regards Yafang