linux-kernel - Re: [PATCH -RFC 0/2] mm/ext4: avoid data corruption when extending DIO write race with buffered read

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Message-ID: <ZXBm95si+j7lmalf@infradead.org>
Date:   Wed, 6 Dec 2023 04:20:07 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Dave Chinner <david@...morbit.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Baokun Li <libaokun1@...wei.com>, Jan Kara <jack@...e.cz>,
        linux-mm@...ck.org, linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, willy@...radead.org,
        akpm@...ux-foundation.org, ritesh.list@...il.com,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        yangerkun@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH -RFC 0/2] mm/ext4: avoid data corruption when extending
 DIO write race with buffered read

On Wed, Dec 06, 2023 at 09:34:49PM +1100, Dave Chinner wrote:
> Largely they were performance problems - unpredictable IO latency
> and CPU overhead for IO meant applications would randomly miss SLAs.
> The application would see IO suddenly lose all concurrency, go real
> slow and/or burn lots more CPU when the inode switched to buffered
> mode.
> 
> I'm not sure that's a particularly viable model given the raw IO
> throughput even cheap modern SSDs largely exceeds the capability of
> buffered IO through the page cache. The differences in concurrency,
> latency and throughput between buffered and DIO modes will be even
> more stark itoday than they were 20 years ago....

The question is what's worse:  random performance drops or random
corruption.  I suspect the former is less bad, especially if we have
good tracepoints to pin it down.