linux-kernel - [Regerssion] [KSM] KSM CPU overhead in 6.16+ kernel compared to <=6.15 versions ("folio_walk

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Message-ID: <020cf8de6e773bb78ba7614ef250129f11a63781@murena.io>
Date: Mon, 13 Oct 2025 09:22:00 +0000
From: craftfever@...ena.io
To: akpm@...ux-foundation.org, david@...hat.com, xu.xin16@....com.cn,
 chengming.zhou@...ux.dev
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 regressions@...ts.linux.dev
Subject: [Regerssion] [KSM] KSM CPU overhead in 6.16+ kernel compared to
 <=6.15 versions ("folio_walk_start" kernel object overhead)

I've posted about that problem already on bigzilla (#220599), but maintainers asked to post issues on maillist.
The problem with freezes during KSM page scanning with certain processes like Chromium with huge virtual memory size amount was fized in 6.17.1 compared to 6.16.x/6.17, but problem with huge CPU overhead is present there. Compared to Linux <=6.15, where the overhead is much lighter anad there no much CPU consuming during KSM scanning, there is "folio_walk_start" kernel object is present (which I reviewed with "perf top" command) that is not present in versions <=6.15 during KSM work and which is in work starting from Linux 6.16. This method very resource-consuming compared to algorithm used in <=6.15 versions. Is there a kernel parameter to disable it or it needs more optimization?

I'm using MemoryKSM setting in systemd in user@...rvice for KSM process merging and it very light on <=6.15 ver., but CPU consuming on 6.16+ (6.17.1 without freezes) due to reasons said above.