From: "Huang\, Ying" <ying.huang@intel.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>,
Tim Chen <tim.c.chen@linux.intel.com>, "Huang\,
Ying" <ying.huang@intel.com>, <dave.hansen@intel.com>,
<ak@linux.intel.com>, <aaron.lu@intel.com>, <linux-mm@kvack.org>,
<linux-kernel@vger.kernel.org>, Hugh Dickins <hughd@google.com>,
Shaohua Li <shli@kernel.org>, Minchan Kim <minchan@kernel.org>,
Rik van Riel <riel@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Hillf Danton <hillf.zj@alibaba-inc.com>,
Christian Borntraeger <borntraeger@de.ibm.com>
Subject: Re: [PATCH v5 2/9] mm/swap: Add cluster lock
Date: Thu, 12 Jan 2017 09:47:51 +0800 [thread overview]
Message-ID: <8760ll122g.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <20170111151526.e905b91d6f1ee9f21e6907be@linux-foundation.org> (Andrew Morton's message of "Wed, 11 Jan 2017 15:15:26 -0800")
Hi, Andrew,
Andrew Morton <akpm@linux-foundation.org> writes:
> On Wed, 11 Jan 2017 16:07:29 -0700 Jonathan Corbet <corbet@lwn.net> wrote:
>
>> On Wed, 11 Jan 2017 15:00:29 -0800
>> Andrew Morton <akpm@linux-foundation.org> wrote:
>>
>> > hm, bit_spin_lock() is a nasty thing. It is slow and it doesn't have
>> > all the lockdep support.
>> >
>> > Would the world end if we added a spinlock to swap_cluster_info?
>>
>> FWIW, I asked the same question in December, this is what I got:
>>
>> ...
>>
>> > > Why the roll-your-own locking and data structures here? To my naive
>> > > understanding, it seems like you could do something like:
>> > >
>> > > struct swap_cluster_info {
>> > > spinlock_t lock;
>> > > atomic_t count;
>> > > unsigned int flags;
>> > > };
>> > >
>> > > Then you could use proper spinlock operations which, among other things,
>> > > would make the realtime folks happier. That might well help with the
>> > > cache-line sharing issues as well. Some of the count manipulations could
>> > > perhaps be done without the lock entirely; similarly, atomic bitops might
>> > > save you the locking for some of the flag tweaks - though I'd have to look
>> > > more closely to be really sure of that.
>> > >
>> > > The cost, of course, is the growth of this structure, but you've already
>> > > noted that the overhead isn't all that high; seems like it could be worth
>> > > it.
>> >
>> > Yes. The data structure you proposed is much easier to be used than the
>> > current one. The main concern is the RAM usage. The size of the data
>> > structure you proposed is about 80 bytes, while that of the current one
>> > is about 8 bytes. There will be one struct swap_cluster_info for every
>> > 1MB swap space, so for 1TB swap space, the total size will be 80M
>> > compared with 8M of current implementation.
>
> Where did this 80 bytes come from? That swap_cluster_info is 12 bytes
> and could perhaps be squeezed into 8 bytes if we can get away with a
> 24-bit "count".
Sorry, I made a mistake when measuring the size of swap_cluster_info
when I sent that email, because I turned on the lockdep when measuring.
I have sent out a correction email to Jonathan when I realized that
later.
So the latest size measuring result is:
If we use bit_spin_lock, the size of cluster_swap_info will,
- increased from 4 bytes to 8 bytes on 64 bit platform
- keep as 4 bytes on 32 bit platform
If we use normal spinlock (queue spinlock), the size of cluster_swap_info will,
- increased from 4 bytes to 8 bytes on 64 bit platform
- increased from 4 bytes to 8 bytes on 32 bit platform
So the difference occurs on 32 bit platform. If the size increment on
32 bit platform is OK, then I think it should be good to use normal
spinlock instead of bit_spin_lock. Personally, I am OK for that. But I
don't know whether there will be some embedded world people don't like
it.
Best Regards,
Huang, Ying
next prev parent reply other threads:[~2017-01-12 1:48 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-11 17:55 [PATCH v5 0/9] mm/swap: Regular page swap optimizations Tim Chen
2017-01-11 17:55 ` [PATCH v5 1/9] mm/swap: Fix kernel message in swap_info_get() Tim Chen
2017-01-11 17:55 ` [PATCH v5 2/9] mm/swap: Add cluster lock Tim Chen
2017-01-11 23:00 ` Andrew Morton
2017-01-11 23:07 ` Jonathan Corbet
2017-01-11 23:15 ` Andrew Morton
2017-01-12 1:47 ` Huang, Ying [this message]
2017-01-12 1:58 ` Andrew Morton
2017-01-12 2:51 ` Huang, Ying
2017-01-14 4:37 ` [Update][PATCH " Huang, Ying
2017-01-12 1:23 ` [PATCH " Huang, Ying
2017-01-11 17:55 ` [PATCH v5 3/9] mm/swap: Split swap cache into 64MB trunks Tim Chen
2017-01-11 23:09 ` Andrew Morton
2017-01-11 23:19 ` Andi Kleen
2017-01-12 16:47 ` Tim Chen
2017-01-11 17:55 ` [PATCH v5 4/9] mm/swap: skip read ahead for unreferenced swap slots Tim Chen
2017-01-11 17:55 ` [PATCH v5 5/9] mm/swap: Allocate swap slots in batches Tim Chen
2017-01-11 17:55 ` [PATCH v5 6/9] mm/swap: Free swap slots in batch Tim Chen
2017-01-11 17:55 ` [PATCH v5 7/9] mm/swap: Add cache for swap slots allocation Tim Chen
2017-01-17 2:55 ` [Update][PATCH " Huang, Ying
2017-01-17 10:16 ` Michal Hocko
2017-01-17 17:24 ` Chen, Tim C
2017-01-17 20:03 ` Michal Hocko
2017-01-17 20:31 ` Chen, Tim C
2017-01-17 21:42 ` Tim Chen
2017-01-18 12:45 ` Michal Hocko
2017-01-18 18:03 ` Tim Chen
2017-01-18 18:15 ` Michal Hocko
2017-01-11 17:55 ` [PATCH v5 8/9] mm/swap: Enable swap slots cache usage Tim Chen
2017-01-11 17:55 ` [PATCH v5 9/9] mm/swap: Skip readahead only when swap slot cache is enabled Tim Chen
2017-01-16 12:02 ` [PATCH v5 0/9] mm/swap: Regular page swap optimizations Michal Hocko
2017-01-17 1:06 ` Huang, Ying
2017-01-17 7:49 ` Michal Hocko
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