linux-kernel - Re: [PATCH] filesystem-dax: Disable PMD support

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Date:   Thu, 27 Jun 2019 05:34:15 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-nvdimm@...ts.01.org, Jan Kara <jack@...e.cz>,
        stable@...r.kernel.org, Robert Barror <robert.barror@...el.com>,
        Seema Pandit <seema.pandit@...el.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] filesystem-dax: Disable PMD support

On Wed, Jun 26, 2019 at 05:15:45PM -0700, Dan Williams wrote:
> Ever since the conversion of DAX to the Xarray a RocksDB benchmark has
> been encountering intermittent lockups. The backtraces always include
> the filesystem-DAX PMD path, multi-order entries have been a source of
> bugs in the past, and disabling the PMD path allows a test that fails in
> minutes to run for an hour.

On May 4th, I asked you:

Since this is provoked by a fatal signal, it must have something to do
with a killable or interruptible sleep.  There's only one of those in the
DAX code; fatal_signal_pending() in dax_iomap_actor().  Does rocksdb do
I/O with write() or through a writable mmap()?  I'd like to know before
I chase too far down this fault tree analysis.