linux-kernel - Re: [RFC] mm: khugepaged: use largest enabled hugepage order for min_free

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Message-ID: <83afc94d-707e-4da2-830c-e5fcfd93374d@lucifer.local>
Date: Sat, 7 Jun 2025 09:44:47 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Usama Arif <usamaarif642@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, david@...hat.com,
        linux-mm@...ck.org, hannes@...xchg.org, shakeel.butt@...ux.dev,
        riel@...riel.com, ziy@...dia.com, baolin.wang@...ux.alibaba.com,
        Liam.Howlett@...cle.com, npache@...hat.com, ryan.roberts@....com,
        dev.jain@....com, hughd@...gle.com, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, kernel-team@...a.com
Subject: Re: [RFC] mm: khugepaged: use largest enabled hugepage order for
 min_free_kbytes

OK a 'reviewlet' :P (have to say I like this terminology...)

I see we are already ostensibly 'dynamic' in that hugepage_pmd_enabled() changes
our algorithm.

So my comments about dynamic alterting are probably not quite valid. Are we not
in a weird situation where, with mTHP-only enabled we just use
calculate_min_free_kbytes()??

That probably needs addressing (perhaps separately...)

Lord I hate how we do this (not your fault!)

Rest of review still applicable :>)

Thanks for raising these important issues, while I am raising technical
criticism of the patch, I do very much think you're identifying a real (and
really very significant for those using v. large page table sizes) problem we
need to address one way or another.

Cheers, Lorenzo