On Fri, Apr 05, 2013 at 08:17:00AM +0800, Simon Jeons wrote: > Hi Minchan, > On 01/23/2013 03:58 PM, 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 > >>6. Better swap prefetch algorithm. Besides item 3, sequentially accessed pages > >>aren't always in LRU list adjacently, so page reclaim will not swap such pages > >>in adjacent storage sectors. This makes swap prefetch hard. > >One of problem is LRU churning and I wanted to try to fix it. > >http://marc.info/?l=linux-mm&m=130978831028952&w=4 > > I'm interested in this feature, why it didn't merged? what's the > fatal issue in your patchset? > http://lwn.net/Articles/449866/ There wasn't any fatal issue, AFAIRC but some people had a concern about balancing between code complexity and benefit and dragged for a long time and I lost interest. > You mentioned test script and all-at-once patch, but I can't get > them from the URL, could you tell me how to get it? You can google it and google will find it in a few second. http://www.filewatcher.com/b/ftp/ftp.cs.huji.ac.il/mirror/linux/kernel/linux/kernel/people/minchan/inorder_putback/v4-0.html -- Kind regards, Minchan Kim -- 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>