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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-90c9360b07csm64972756d6.17.2026.08.24.08.09.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Aug 2026 08:09:55 -0700 (PDT) Date: Mon, 24 Aug 2026 11:09:54 -0400 From: Gregory Price To: Matthew Wilcox Cc: linux-mm@kvack.org, akpm@linux-foundation.org, edumazet@google.com, linux-kernel@vger.kernel.org, kernel-team@meta.com, stable@vger.kernel.org, david@kernel.org, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, syzbot+0dbf6d295b3350944f0b@syzkaller.appspotmail.com Subject: Re: [PATCH] mm/mempolicy: refcount the weighted interleave state instead of copying it Message-ID: References: <20260821104043.f692421fec915c0c5bc1fbe6@linux-foundation.org> <20260824024117.1755899-1-gourry@gourry.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 7EDABC0006 X-Stat-Signature: coxf1ik8fd9uicie18dz49ekhzkmf3hk X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1787584197-873613 X-HE-Meta: U2FsdGVkX1/Dfrqtzl5gJJ77lH1QVHeqHsykebSkT4vBLLxCY2XSYumdR76tbnCGcFmLcY+ZIkTCauTd6vR9xIL7KEJPQq9LWaf6bkxtokkHM9U8aunqEotUynt5Z7/I95ItdjBcOG6VYq6D4DtgUBR7Dx2NK5woy/5OO5qFA/wh6qyIG4LMTMjuh8sybLWM8mF9HF/QiyWtf08Bn3YO2gytkRtBU67fsk1UaZp5/7QNiaur4hkpwpgzWxRQt3NXPB3wh30R9Y9te1I963cZCN2wvUAQCD1OE7zextvOQCqyueYhhgj3/sf/G9xVqKxLtxCIxcT2atO1IIehvpwuMaonf3EdLy9kB9QxEHBqB9YwwjtrnhA8icGzclY2e9VYj8WmDlQPz8UZjj+3Vbmd8fSvi0/GDH1JYgZLvK7CEUKnfLnNv5xoVxfNTXY2EsAxC61HQEIP4K7Qp+uik4OfJiX9BCJKjNXTzPu0YO+sGtWOjUp76ufSY0JUDehVQPIODHNFbSqssyF2r4C6Uce39uyNsrEElvON7lyYiDfpTGlEGImdXQDmvENXiNDCRtAufKbDrBLiIR+/Lf0tDcPsqHYOhbsYvaS5JhJapr4hpm9UTqjFhfmzS8BzwEjlEmgRqcjl/UsoDe9AzpE+7O29tpH72/KtdBnjdjRJaE8ub14xLu8FTnNqX0JEV+iSbYasVhob1nQbWywY63fGfnAQKLYEY6nCanLw7Vj1NVFarJDhdr72Wuh2+L+9BRhpekrQUn2En+O8H/yZY87vQmyY6JPfBdrSSoCbpDOOFM47CbnrLyPP9NmwcoorNxl8i8L2JdTtLcb7mL6FPvWRL/sd2tmOK8XnN7jxb+l+mSK6RIqvetF6IanOc/Gk/CBoHpU9I029cs3c8r003CgGiKBqyBvR3If1VG+pVT8D4UYXShEiTVbn1ntGOkjxyESUuz1B6roy3e3OQ8IPjHVtWBT dRJlksM6 MTR3ECLHOWHkQbaRIiR4ldCA2/6VzYgA/0R/PzAg7TgTJH/zMEkVVlvSV7QwGOnZs8fOQkb/rY7/WYbzx+r2A+gcFjSezvGaCDCLPufxJNGbwq/debuiFeMCst2zai4wQ2M0kKf2FGrrsrTcFc7Ya+r/zWjSGt7aJUwBp8EKCWznSraJWGIJJMa8twh41Hkse/nVnatezGKbOxw0gsUvWafog6lH0/UyRiOGhk5u+40AaqyHQP2d0M1gVuSutSFfLVMhrmO1NNQPtMdjPh2shaTwlh/pEs197KiBGiVSLlWRi+CZs6ZxZTsLgPDbaeM1LinB0JCrxNfJ6eo4REJtPcvUmiTAiO2E6rhU6pHVZn/2h8FXGY5dSZ3E6RQ/9oFSyzv1wFgBT8gz13ZsW4YincvDaurSJJHggcfPNwuRRAMfXkyoAsR9Gz3E651FLMSe4fQir80mVC9rgbJH7ePmREQP/uA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Aug 23, 2026 at 11:52:55PM -0400, Gregory Price wrote: > On Mon, Aug 24, 2026 at 04:06:03AM +0100, Matthew Wilcox wrote: > > On Sun, Aug 23, 2026 at 10:41:17PM -0400, Gregory Price wrote: > > > > Bit of a shame to take/put a refcount on every memory allocation. That > > seems like it might hurt (even being on a different cacheline). Would > > it make more sense to use SRCU for this? > > Bulk allocation - from some measurements it's about once per 100-pages > on average. Looking back at the data I was getting about 41 refs per > 4096 pages (16MB chunks). > > Have to imagine there's other cache fighting in that stack too. > > I'm less familiar with the rules around SRCU so i shied away from it, > but I will take a look. > I will update to the new fast srcu mechanism, but it'll prevent backporting beyond 6.18. Best to backport the gfp fix and update to srcu in normal cadence. Will submit separately. ~Gregory