Minchan Kim <minc...@kernel.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
