linux-kernel - Re: [PATCH 00/14] Reduce preallocations for maple tree

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Message-ID: <9f4c10bb-ee7c-cd41-f1b9-c1a7a1a562fd@google.com>
Date:   Mon, 5 Jun 2023 19:41:22 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Peng Zhang <zhangpeng.00@...edance.com>,
        "Yin, Fengwei" <fengwei.yin@...el.com>,
        maple-tree@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, "Liu, Yujie" <yujie.liu@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 00/14] Reduce preallocations for maple tree

On Mon, 5 Jun 2023, Liam R. Howlett wrote:
> 
> You mean "mm: update validate_mm() to use vma iterator" here I guess.  I
> have it as a different commit id in my branch.
> 
> I 'restored' some of the checking because I was able to work around not
> having the mt_dump() definition with the vma iterator.  I'm now
> wondering how wide spread CONFIG_DEBUG_VM is used and if I should not
> have added these extra checks.

Most CONFIG_DEBUG_VM checks are quite cheap, mostly VM_BUG_ONs for
easily checked conditions.  If validate_mm() is still the kind of thing
it used to be, checking through every vma on every mmap operation, please
don't bring that into CONFIG_DEBUG_VM - it distorts performance too much,
so always used to be under a separate CONFIG_DEBUG_VM_RB instead.

Hugh