From: Hugh Dickins <hughd@google.com>
To: Shaohua Li <shaohua.li@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
lkml <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>, Andi Kleen <andi@firstfloor.org>,
"Zhang, Yanmin" <yanmin.zhang@intel.com>
Subject: Re: [PATCH]shmem: reduce one time of locking in pagefault
Date: Thu, 8 Jul 2010 18:28:20 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.1.00.1007081814420.1132@tigran.mtv.corp.google.com> (raw)
In-Reply-To: <20100707013919.GA22097@sli10-desk.sh.intel.com>
On Wed, 7 Jul 2010, Shaohua Li wrote:
> On Wed, Jul 07, 2010 at 09:32:54AM +0800, Andrew Morton wrote:
> >
> > The patch doesn't make shmem_getpage() any clearer :(
:)
> >
> > shmem_inode_info.lock appears to be held too much. Surely
> > lookup_swap_cache() didn't need it (for example).
> >
> > What data does shmem_inode_info.lock actually protect?
> As far as my understanding, it protects shmem swp_entry, which is most used
> to support swap. It also protects some accounting. If no swap, the lock almost
> can be removed like tiny-shmem.
That's right: shmem_info_info.lock protects what's in shmem_inode_info,
plus what hangs off it (the shmem_swp blocks).
We want that lock across the lookup_swap_cache() to be sure that what we
find is still what we want (otherwise another thread might bring it out
of swap and that swap be reused for something else) - the page lock is
good once you have a page to lock, but until then.... I guess could be
done by dropping the lock then retaking and rechecking after, but that
would go right against the grain of this patch.
Hugh
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next prev parent reply other threads:[~2010-07-09 1:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-07-07 1:15 Shaohua Li
2010-07-07 1:32 ` Andrew Morton
2010-07-07 1:39 ` Shaohua Li
2010-07-09 1:28 ` Hugh Dickins [this message]
2010-07-09 1:13 ` Hugh Dickins
2010-07-09 2:52 ` Shaohua Li
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