From: Andrew Morton <akpm@osdl.org>
To: Andrea Arcangeli <andrea@suse.de>
Cc: linux-kernel@vger.kernel.org, hugh@veritas.com
Subject: Re: smp race fix between invalidate_inode_pages* and do_no_page
Date: Tue, 13 Dec 2005 13:02:27 -0800 [thread overview]
Message-ID: <20051213130227.2efac51e.akpm@osdl.org> (raw)
In-Reply-To: <20051213193735.GE3092@opteron.random>
Andrea Arcangeli <andrea@suse.de> wrote:
>
> ...
>
> Clearly taking the page lock in do_no_page would fix it too, but it
> would destroy the scalability of page faults.
It's always bugged me that filemap_nopage() doesn't lock the page. There
might be additional uglies which could be tidied up if we were to do so.
The scalability loss would happen if there are multiple processes/threads
faulting in the same page I guess. I wonder how important that would be.
I suppose that even if we did lock the page in filemap_nopage(), the
coverage isn't sufficient here - it needs to extend into do_no_page()?
> The seqschedlock instead
> is 100% smp scalable in the fast path (exactly like RCU and seqlocks),
> and it's lightweight in the write path too and it doesn't introducing
> latencies in freeing memory.
Why this rather than down_read/down_write? We might even be able to hoist
ext3_inode's i_truncate_sem into the address_space, for zero space cost on
most Linux inodes (dunno).
Is there some way in which we can use mapping->truncate_count to tell
do_no_page() that it raced with invalidate()? By checking it after the pte
has been established?
> My main concern is the yield() instead of a waitqueue but perhaps that
> can be improved somehow (I didn't think much about it yet). Not sure if
> a waitqueue would be better off inside or outside the seqschedlock, but
> I believe these are secondary matters, in practice it should never
> trigger.
yield() is pretty sucky.
next prev parent reply other threads:[~2005-12-13 21:02 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-13 19:37 smp race fix between invalidate_inode_pages* and do_no_page Andrea Arcangeli
2005-12-13 21:02 ` Andrew Morton [this message]
2005-12-13 21:14 ` Andrea Arcangeli
2005-12-16 13:51 ` Andrea Arcangeli
2006-01-10 6:24 ` Andrea Arcangeli
2006-01-10 6:48 ` Andrea Arcangeli
2006-01-11 4:08 ` Nick Piggin
2006-01-11 8:23 ` Andrea Arcangeli
2006-01-11 8:51 ` Andrew Morton
2006-01-11 9:02 ` Andrea Arcangeli
2006-01-11 9:06 ` Andrew Morton
2006-01-11 9:13 ` Andrea Arcangeli
2006-01-11 20:49 ` Hugh Dickins
2006-01-11 21:05 ` Andrew Morton
2006-01-13 7:35 ` Nick Piggin
2006-01-13 7:47 ` Andrew Morton
2006-01-13 10:37 ` Nick Piggin
2006-03-31 12:36 ` Andrea Arcangeli
2006-04-02 5:17 ` Nick Piggin
2006-04-02 5:21 ` Andrew Morton
2006-04-07 19:18 ` Hugh Dickins
2006-01-11 9:39 ` Nick Piggin
2006-01-11 9:34 ` Nick Piggin
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