On Mon, Jan 28, 2013 at 4:37 PM, Kyungmin Park <kmpark@xxxxxxxxxxxxx> wrote: > On Sun, Jan 27, 2013 at 11:18 PM, Shaohua Li <shli@xxxxxxxxxx> wrote: >> On Sat, Jan 26, 2013 at 01:40:55PM +0900, Kyungmin Park wrote: >>> Hi, >>> >>> On 1/24/13, Simon Jeons <simon.jeons@xxxxxxxxx> wrote: >>> > Hi Minchan, >>> > On Wed, 2013-01-23 at 16:58 +0900, Minchan Kim wrote: >>> >> On Tue, Jan 22, 2013 at 02:53:41PM +0800, Shaohua Li wrote: >>> >> > Hi, >>> >> > >>> >> > Because of high density, low power and low price, flash storage (SSD) is >>> >> > a good >>> >> > candidate to partially replace DRAM. A quick answer for this is using >>> >> > SSD as >>> >> > swap. But Linux swap is designed for slow hard disk storage. There are a >>> >> > lot of >>> >> > challenges to efficiently use SSD for swap: >>> >> >>> >> Many of below item could be applied in in-memory swap like zram, zcache. >>> >> >>> >> > >>> >> > 1. Lock contentions (swap_lock, anon_vma mutex, swap address space >>> >> > lock) >>> >> > 2. TLB flush overhead. To reclaim one page, we need at least 2 TLB >>> >> > flush. This >>> >> > overhead is very high even in a normal 2-socket machine. >>> >> > 3. Better swap IO pattern. Both direct and kswapd page reclaim can do >>> >> > swap, >>> >> > which makes swap IO pattern is interleave. Block layer isn't always >>> >> > efficient >>> >> > to do request merge. Such IO pattern also makes swap prefetch hard. >>> >> >>> >> Agreed. >>> >> >>> >> > 4. Swap map scan overhead. Swap in-memory map scan scans an array, which >>> >> > is >>> >> > very inefficient, especially if swap storage is fast. >>> >> >>> >> Agreed. >>> >> >>> >>> 5. SSD related optimization, mainly discard support. >>> >>> Now swap codes are based on each swap slots. it means it can't >>> optimize discard feature since getting meaningful performance gain, it >>> requires 2 pages at least. Of course it's based on eMMC. In case of >>> SSD. it requires more pages to support discard. >>> >>> To address issue. I consider the batched discard approach used at filesystem. >>> *Sometime* scan all empty slot and it issues discard continuous swap >>> slots as many as possible. >> >> I posted a patch to make discard async before, which is almost good to me, though we >> still discard a cluster. >> http://marc.info/?l=linux-mm&m=135087309208120&w=2 > > I found your previous patches, It's almost same concept as batched > discard. Now I'm testing your patches. > BTW, which test program do you use? Now we just testing some scenario > and check scenario only. > There's no generic tool to measure improved performance gain. > > After test, I'll share the results. Updated, it has good performance gain than previous one about 4 times. Feel free to add. Tested-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> > > Thank you, > Kyungmin Park -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>