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Date:   Tue, 15 Sep 2020 11:47:45 -0700
From:   Linus Torvalds <>
To:     Matthieu Baerts <>
Cc:     Michael Larabel <>,
        Matthew Wilcox <>,
        Amir Goldstein <>,
        "Ted Ts'o" <>,
        Andreas Dilger <>,
        Ext4 Developers List <>,
        Jan Kara <>,
        linux-fsdevel <>
Subject: Re: Kernel Benchmarking

On Tue, Sep 15, 2020 at 11:27 AM Linus Torvalds
<> wrote:
> Every one of them is in the "io_schedule()" in the filemap_fault()
> path, although two of them seem to be in file_fdatawait_range() rather
> than in the lock_page() code itself (so they are also waiting on a
> page bit, but they are waiting for the writeback bit to clear).

No, that seems to be just stale entries on the stack from a previous
system call, rather than a real trace. There's no way to reach
file_fdatawait_range() from mlockall() that I can see.

So I'm not entirely sure why the stack trace for two of the processes
looks a bit different, but they all look like they should be in

It's possible those two were woken up (by another CPU) and their stack
is in flux. They also have "wake_up_page_bit()" as a stale entry on
their stack, so that's not entirely unlikely.

So that sysrq-W state shows that yes, people are stuck waiting for a
page, but that wasn't exactly unexpected.


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