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charset=utf-8 Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 4BAB7140016 X-Stat-Signature: g15cirdiob3nwn1685cbcwcktut631n5 X-HE-Tag: 1746025912-904690 X-HE-Meta: U2FsdGVkX1+QwJA8ZuIZlDbs1H79IbVwAMgcsgw/0Hc6BTwDk5e68FLpB591VkCnAolbKbComeV1BglvNib3r0G4PNkzMgn7ZJ+Vu9AhFxm0qrDq+kq/9l0N6IH7j+saoQNa+AT0e3uPZhTZ7doRg5lWfK9SFTldErbxlvDFTuAS79N1enQGqO20rxI9DJgh/B99jd5g7t2O1pqSiwoPxCKRikpsKjTHUHFCQKamR2wBNhh95vOATPcFIuAbK9swKUmcpeQqpRy0tfkzjvCwC0qOelYD7tcZiYGAZe0fGtn7UBSy7fftycLNQvi2/BZtuMGE5WHsIMir0fnLHxJB096pLgzb1kvm5adN3dvlrYsp0btRWPSYU8dMT7qgXKMHh266e9aHZbE4QV+KZrchrpEHKUx0OQEVb1oYsORDOiLec76Y/d7JQ2NLfIFHDMFwq1lJGZJ/z6DYVZ6+wL97Or55X3tID9Z7q/KxpouJaPBGkNpmvary+EcF9SUvVAzLbaVDz7Amrt8noNzWWmIDHbgIJmjYE+a0umlRj+QXKQECZsSitqmEhRkDMPwk784QDMmS7W4nfQ5Wl/MrugSKFEav/sKXcdbHIQiCpRhR38TMMsz5RISYtdod6wDKL6tWSpJRo4m8gMyFgjZfqwXIYwLSsvV7x7jPdGXnumjDNgfDppmcE+frnQNNKoHkQRq5I8ADzgSztr0gx1dIsqk/QV4Tx8fl/vnKoJg+C27XzpD653+jRz42c0ULy5wvkT0D0epZ2kozSzlBHPKbeOKXAYUb1Db1C1W9bD7QWTjlrEoLh2L7uZ2P1rQR/rCEi2t3ynHXhM3Lbplifmb2e0CRlPQG2X1yYciN7HcmbGyNhEndGOO5ANRYAN7ztZzFiO+NcHo3LwhopBzvNMQBvy+yM14RMmYRb1wttQs+Ql1PP0dXp3NlM5gus2YRkZl+yXLcU0+NZlvaNyW7ZPoDchJ qLE3OhfC oO2+Ht7vJuQ10SK52X4zsmMCd9V0iXk8Gl+C+/VVQ6viy7P1csevEogPsYW1UI0ZByFGvDhhhZqTauG1pXoEbtp5rhvai2ORvI+WtRxDJKKkE7AU7b5I34BcU8ZzhxupOMhLZSTd7OT0fmEC84L5M+Kzb35GHe1o7YR2nSdV8eCTfUSCpIutn8zdHgefQJE28ZkL18n8wP8Rua/ovPOBa71MwcgN68k6/+SB3BgP0UxCi8zRvKYDQWkJOumb1Q5R8GH4GkwJo28I3eTO85kx2FQwzKma04wPWDq4BXuqggeCtV74BT7IrrKo63w== 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 2025-04-29 21:37:26 [-0700], Shakeel Butt wrote: > > > - if (gfpflags_allow_spinning(gfp_mask)) > > > - local_lock_irqsave(&memcg_stock.stock_lock, flags); > > > - else if (!local_trylock_irqsave(&memcg_stock.stock_lock, flags)) > > > + if (nr_pages > MEMCG_CHARGE_BATCH || > > > + !local_trylock_irqsave(&memcg_stock.stock_lock, flags)) > > > > I don't think it's a good idea. > > spin_trylock() will fail often enough in PREEMPT_RT. > > Even during normal boot I see preemption between tasks and they > > contend on the same cpu for the same local_lock==spin_lock. > > Making them take slow path is a significant behavior change > > that needs to be carefully considered. > > I didn't really think too much about PREEMPT_RT kernels as I assume > performance is not top priority but I think I get your point. Let me Not sure if this is performance nor simply failing to allocate memory. > explain and correct me if I am wrong. On PREEMPT_RT kernel, the local > lock is a spin lock which is actually a mutex but with priority > inheritance. A task having the local lock can still get context switched > (but will remain on same CPU run queue) and the newer task can try to > acquire the memcg stock local lock. If we just do trylock, it will > always go to the slow path but if we do local_lock() then it will sleeps > and possibly gives its priority to the task owning the lock and possibly > make that task to get the CPU. Later the task slept on memcg stock lock > will wake up and go through fast path. So far correct. On PREEMPT_RT a task with spinlock_t or local_lock_t can get preempted while owning the lock. The local_lock_t is a per-CPU lock. Sebastian