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Tue, 30 Sep 2025 03:18:20 -0700 (PDT) X-Google-Smtp-Source: AGHT+IE3ZyM9t5bViNq/9tSXepHz486aMuBktyiQyddVglqgRvUr8MS3voy5nEWgaNyrtI+mrjb6Ig== X-Received: by 2002:adf:8b47:0:b0:424:21ff:5151 with SMTP id ffacd0b85a97d-42421ff535fmr1705043f8f.5.1759227500105; Tue, 30 Sep 2025 03:18:20 -0700 (PDT) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([185.107.56.35]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-40fb9e1b665sm22006951f8f.27.2025.09.30.03.18.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Sep 2025 03:18:19 -0700 (PDT) Message-ID: <2bf22dc5213ada5339d85744c348da9558f25e3d.camel@redhat.com> Subject: Re: [PATCH v2 2/4] rseq: Run the mm_cid_compaction from rseq_handle_notify_resume() From: Gabriele Monaco To: Thomas Gleixner , Mathieu Desnoyers , Ingo Molnar , Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , linux-mm@kvack.org, "Paul E. McKenney" Date: Tue, 30 Sep 2025 12:18:18 +0200 In-Reply-To: <87tt0k3oks.ffs@tglx> References: <87tt0k3oks.ffs@tglx> Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0BrZXJuZWwub3JnPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmjKX2MCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfIQuAD+JulczTN6l7oJjyroySU55Fbjdvo52xiYYlMjPG7dCTsBAMFI7dSL5zg98I+8 cXY1J7kyNsY6/dcipqBM4RMaxXsOtCRHYWJyaWVsZSBNb25hY28gPGdtb25hY29AcmVkaGF0LmNvb T6InAQTFgoARAIbAwUJBaOagAULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgBYhBMrKEfgLgd0WcK eo9u9KbElYeE3yBQJoymCyAhkBAAoJEO9KbElYeE3yjX4BAJ/ETNnlHn8OjZPT77xGmal9kbT1bC1 7DfrYVISWV2Y1AP9HdAMhWNAvtCtN2S1beYjNybuK6IzWYcFfeOV+OBWRDQ== User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Gex1nAoLMt6_FntrW3RYJZC_49F-G8S9Z4m4F8eXurI_1759227500 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: 83xxm9oqy8htkrpwama98hkqpoakjc16 X-Rspam-User: X-Rspamd-Queue-Id: 711A820014 X-Rspamd-Server: rspam10 X-HE-Tag: 1759227503-120079 X-HE-Meta: U2FsdGVkX18ozdtfRJMwDMtbhQFBMn8jiczQQUZw2WG/GU2sZrLmLtUAatZh2Gz45TLd5jB+0A8qOBeRwoB8IFT2PWtNvQg2y/s+nc8hmW2eDsyvFiGV9ctR7y0isxPT7PE0NLMVA6ZGdubizk+mr5Mg/jXEpzWrQyPLJxTUjRbfeklYBXr6BoQT/hVrt0qo/6zdwMMy9dWnmkxDmxfG8YBwZ5b43pl2gIG9X7CBUDFImP2AzRLWbwbvcCbju3DTv5yygDblzYMKF81TgFaa/MIrAwtw1uDk9nUrib326JJ75b79BNZjy5jumnQlSfVhJk+0Jd+BZXH9EfIf8Ts0UxwyBTB+35w2kDBJ2TeqI91qLYi3b9dOl4Um+AMa89mR9ZDHH9e2nMzIRmsGYFu7e5nARFy65eNvCLNE6zvRgUZTJQW5zaqnEZ4dgzfvvSDA6CU4bB0oXYqc+9XF1GXx8t0mRnZ/5VTTLjMEnK1+oVMk/nUcZNgyMP6bVSVK0DdbUY+55tNhM3mnM7l7yTdy6YLoqIR4BkUKUnGr8ZPZD4gD+biWky8DM8SYRdAEvq2+w5PXaC0qFFYyIOYL/UCtB+ZlGKTfTV9FileKF/DMNe2ClsCQwZ1W6+TT98/kHee7rNyWb/zJAwrQyeMnUCE5h8MKmxCJghsXqeuEtjKsEcJMwiSssrU/WwlYycUL9MDY1eu1NFoGKUgDa2ODuNgcW67ygzcR97WVHvVsOftGP4xFAeLe9nI/K7n3xRYYy81uUpBvST9aVk0oNno4t1+xeASrZ1UmymOYTxB+rKbIVU1DTCG95DxnPDkXiSh0etPDYg9BY3m2DzKtCmW5lbQcSiI+6N74WPJsLMW7bXt+I9gJICxM+9Ta71x3LEk+az5GPPJaVi3OMi5x4DwNayNRTTdQ0MzPuYH1AjsFn/2yOaYqd/+Xq7iU1E/JFsUunzctizcKrjmLiLsBJ8eS+ZU jzEcGE3t vyy3pxiriAPRT5TMZhG6793nG2OFTefOpANSHF+EzdGuw2WygL42qoVK4MDOSauV4bSnRs2K3slaxI5tvrHwYtJV1FLdYgEQu+6c1DfyOfDNV0qNRV3LILMcLtLQLTKFmJ77YvIql7FwcLZ2X2JOPUbv5NniuQnnWgbyfBqGqG4hDKB6I0LkkS9xFyx66lpxpjeCY/BrhD3hRSkJ0Ed5RmpMo7E8pMAtkMyQhGOE9/G9wk44ThC924pzDSNPpGQJ4Jn72eQ3zh3DWqIgtZbdfIXe2BLc8C0gVCkDg6H2wF+LFoRFQzWOHW+N0ZVSGqBYVvhxUgnk1YTobxyGNcJJe+vvqi/38IwUlTvWSsU6ssNrqTSBPrtWVXZlbAfhSxteyCGGLiZwkjdbcO9k= 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, 2025-09-30 at 00:01 +0200, Thomas Gleixner wrote: >=20 > The current overhead of RSEQ is way too high. People have reported 3% > regressions just because glibc uses RSEQ now. So that needs to be > addressed. Moving the RSEQ fastpath to the last point before going back > to user space is the correct thing to do. >=20 > mm cid compaction is a related but orthogonal problem. I just skimmed > your patches and I'm really not convinced that this is the right > approach to solve the problem. >=20 > The main issue with task_mm_cid_work() is that it iterates over all > possible CPUs twice. Your batching just makes the impact smaller, but it > does not really try to change the overall approach to this. Thanks for the thorough explanation and sketch implementation.=C2=A0As I'm = not really confident with rseq I didn't dare changing the compaction logic too much, b= ut clearly your approach of getting compact cid by construction seems the way = to go. I confirm your patch passes the selftest in 4/4 of this series and, obvious= ly, removes the latency I was observing. Thanks, Gabriele