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

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Message-ID: <20210210212228.GF3014244@iweiny-DESK2.sc.intel.com>
Date:   Wed, 10 Feb 2021 13:22:28 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Matthew Wilcox <willy@...radead.org>
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 06:56:06PM +0000, Matthew Wilcox wrote:
> 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?

I can't guarantee it but right now most of the conversions I have worked on are
in FS's.

> 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.

Honestly, I don't feel strongly enough to argue it.

Andrew?  David?  David this is going through your tree so would you feel more
comfortable with 1 or the other?

Ira