From: Andrew Morton <akpm@linux-foundation.org>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Jonathan Corbet <corbet@lwn.net>,
Tim Chen <tim.c.chen@linux.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: Wed, 11 Jan 2017 17:58:12 -0800 [thread overview]
Message-ID: <20170111175812.9e459e4c51502265aad5f2dc@linux-foundation.org> (raw)
In-Reply-To: <8760ll122g.fsf@yhuang-dev.intel.com>
On Thu, 12 Jan 2017 09:47:51 +0800 "Huang\, Ying" <ying.huang@intel.com> wrote:
> >> > 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.
I think that'll be OK - the difference is small and many small systems
disable swap anyway. So can we please try that? Please do describe
the additional overhead (with numbers) in the changelog: "additional
bytes of RAM per GB of swap", for example. And please also rerun the
performance tests, see if we can notice the alleged speed improvements
from switching to a spinlock.
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next prev parent reply other threads:[~2017-01-12 1:58 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
2017-01-12 1:58 ` Andrew Morton [this message]
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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