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Date: Wed, 28 Dec 2016 12:56:23 +0800 From: "Huang\, Ying" <ying.huang@...el.com> To: Minchan Kim <minchan@...nel.org> Cc: "Huang\, Ying" <ying.huang@...el.com>, Tim Chen <tim.c.chen@...ux.intel.com>, Andrew Morton <akpm@...ux-foundation.org>, <dave.hansen@...el.com>, <ak@...ux.intel.com>, <aaron.lu@...el.com>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>, Hugh Dickins <hughd@...gle.com>, Shaohua Li <shli@...nel.org>, Rik van Riel <riel@...hat.com>, Andrea Arcangeli <aarcange@...hat.com>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Vladimir Davydov <vdavydov.dev@...il.com>, Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, Hillf Danton <hillf.zj@...baba-inc.com>, "Christian Borntraeger" <borntraeger@...ibm.com>, Jonathan Corbet <corbet@....net>, <jack@...e.cz> Subject: Re: [PATCH v4 0/9] mm/swap: Regular page swap optimizations Minchan Kim <minchan@...nel.org> writes: > On Wed, Dec 28, 2016 at 11:31:06AM +0800, Huang, Ying wrote: > > < snip > > >> >>> > Frankly speaking, although I'm huge user of bit_spin_lock(zram/zsmalloc >> >>> > have used it heavily), I don't like swap subsystem uses it. >> >>> > During zram development, it really hurts debugging due to losing lockdep. >> >>> > The reason zram have used it is by size concern of embedded world but server >> >>> > would be not critical so please consider trade-off of spinlock vs. bit_spin_lock. >> >>> >> >>> There will be one struct swap_cluster_info for every 1MB swap space. >> >>> So, for example, for 1TB swap space, the number of struct >> >>> swap_cluster_info will be one million. To reduce the RAM usage, we >> >>> choose to use bit_spin_lock, otherwise, spinlock is better. The code >> >>> will be used by embedded, PC and server, so the RAM usage is important. >> >> >> >> It seems you already increase swap_cluster_info 4 byte to support >> >> bit_spin_lock. >> > >> > The increment only occurs on 64bit platform. On 32bit platform, the >> > size is the same as before. >> > >> >> Compared to that, how much memory does spin_lock increase? >> > >> > The size of struct swap_cluster_info will increase from 4 bytes to 16 >> > bytes on 64bit platform. I guess it will increase from 4 bytes to 8 >> > bytes on 32bit platform at least, but I did not test that. >> >> Sorry, I make a mistake during test. The size of struct >> swap_cluster_info will increase from 4 bytes to 8 bytes on 64 bit >> platform. I think it will increase from 4 bytes to 8 bytes on 32 bit >> platform too (not tested). > > Thanks for the information. > To me, it's not big when we consider spinlock's usefullness which helps > cache-line bouncing, lockdep and happy with RT people. Yes. spinlock helps on lockdep and RT, but I don't think it helps cache-line bouncing. > So, I vote spin_lock but I'm not in charge of deciding on that and your > opinion might be different still. If so, let's pass the decision to > maintainer. I have no strong opinion for size change on 32bit platform. But I want to know other people's opinion, especially maintainer's too. > Instead, please write down above content in description for maintainer to > judge it fairly. Sure. Best Regards, Huang, Ying
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