linux-kernel - Re: [v2 PATCH] mm: hugetlb: avoid soft lockup when mprotect to large memory area

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Message-ID: <ef139940-5627-13a3-747a-b030b11e7544@gentwo.org>
Date: Tue, 30 Sep 2025 11:43:12 -0700 (PDT)
From: "Christoph Lameter (Ampere)" <cl@...two.org>
To: Yang Shi <yang@...amperecomputing.com>
cc: Dev Jain <dev.jain@....com>, muchun.song@...ux.dev, osalvador@...e.de, 
    david@...hat.com, akpm@...ux-foundation.org, catalin.marinas@....com, 
    will@...nel.org, anshuman.khandual@....com, carl@...amperecomputing.com, 
    linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org, 
    linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH] mm: hugetlb: avoid soft lockup when mprotect to large
 memory area

On Tue, 30 Sep 2025, Yang Shi wrote:

> > Does it make sense to also do cond_resched() in the huge_pmd_unshare()
> > branch?
> > That also amounts to clearing a page. And I can see for example,
> > zap_huge_pmd()
> > and change_huge_pmd() consume a cond_resched().
>
> Thanks for raising this. I did think about it. But I didn't convince myself
> because shared pmd should be not that common IMHO (If I'm wrong, please feel
> free to correct me). At least PMD can't be shared if the memory is tagged
> IIRC. So I'd like to keep the patch minimal for now and defer adding
> cond_resched() until it is hit by some real life workload.

It would be good to send out a second path that covers the other cases
for discussion.