linux-kernel - Re: [PATCH V2 4/8] mm/highmem: Add VM_BUG_ON() to mem*

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Message-ID: <20210210185606.GF308988@casper.infradead.org>
Date:   Wed, 10 Feb 2021 18:56:06 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Sterba <dsterba@...e.cz>, clm@...com,
        josef@...icpanda.com, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V2 4/8] mm/highmem: Add VM_BUG_ON() to mem*_page() calls

On Wed, Feb 10, 2021 at 08:29:01AM -0800, Ira Weiny wrote:
> And I thought it was a good idea.  Any file system development should have
> tests with DEBUG_VM which should cover Matthew's concern while not having the
> overhead in production.  Seemed like a decent compromise?

Why do you think these paths are only used during file system development?
They're definitely used by networking, by device drivers of all kinds
and they're probably even used by the graphics system.

While developers *should* turn on DEBUG_VM during development, a
shockingly high percentage don't even turn on lockdep.