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Thu, 30 Jan 2025 03:01:19 -0800 (PST) MIME-Version: 1.0 References: <20250128160743.3142544-1-mjguzik@gmail.com> <20250128182932.GC24845@redhat.com> <20250128192224.GD24845@redhat.com> In-Reply-To: <20250128192224.GD24845@redhat.com> From: Mateusz Guzik Date: Thu, 30 Jan 2025 12:01:05 +0100 X-Gm-Features: AWEUYZllMDk_nuIEYPxhctRYXSKBiTMr_ALLK2SDC0mqnQ9op3s_ECgKNubF9rY Message-ID: Subject: Re: [PATCH v2] exit: perform randomness and pid work without tasklist_lock To: Oleg Nesterov Cc: brauner@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Eric W. Biederman" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 456B2A0020 X-Stat-Signature: 68rrc81yfp4q9yjh7gtxfbdot6yiipuj X-Rspam-User: X-HE-Tag: 1738234882-4136 X-HE-Meta: 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 uaCsLutF UVOEsFJo6m5ekpOXF5u0cFBDBmtDjs/X38o3r7B6VXJTTYOUOw+4kpNnfCDDhqZybx+Q9gGSRSe46MK2jGtYB/cacAGgYsqPwhGQGcFhoY4pBcBL9DbkHe2YlR14WKDyK/UXQscAFDHUI0RaPDaa5vuQGnCtfGUQPIr482vsOr5On0+Mzz7CtbEgPF4xsgZ63uLFp/oV3HHJIm932lC2Crwr+E72QhIGNvpfsFFI0jz3YyAdsUHteGRo2zUabIAtPyoreIWsHY6XZfzbaDeleU18G/lyxRY61KzWmP8vKJ9JPNVoC5y5cj58OGZHbNL4ArkQNJFdom6kQFyh3S1pN8yueiA0jRaO71Y9wwTQd52UYxf1apZe0ZkTFEzHiFk6MvmjUpDXlAGh1MRhK+vYafioiR4JwEq+5iSTO X-Bogosity: Ham, tests=bogofilter, spamicity=0.044597, 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, Jan 28, 2025 at 8:22=E2=80=AFPM Oleg Nesterov wro= te: > > On 01/28, Mateusz Guzik wrote: > > > > On Tue, Jan 28, 2025 at 7:30=E2=80=AFPM Oleg Nesterov = wrote: > > > > > no problem, will send a v3 provided there are no issues reported > > concerning the pid stuff > > Great, thanks. > > BTW, I didn't look at the pid stuff yet, I _feel_ that this can be simpli= fied > too, but I am already sleeping, most probably I am wrong. > I looked at pid code apart from the issue at hand. It the lock protecting it uses irq disablement to guard against tasklist_lock users coming from an interrupt. AFAICS this can be legally arranged so that the pidmap_lock is *never* taken while tasklist_lock is held. so far the problematic ordering only stems from free_pid calls (not only on exit), which can all be moved out. this will reduce total tasklist_lock hold time *and* whack the irq trip, speeding this up single-threaded I'll hack it up when I get around to it, maybe this week. btw, with the current patch when rolling with highly parallel thread creation/destruction it is pidmap_lock which is the main bottleneck instead of tasklist_lock --=20 Mateusz Guzik