On Tue, 2013-01-22 at 14:53 +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: > > 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 Which 2 TLB flush? > 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. > 4. Swap map scan overhead. Swap in-memory map scan scans an array, which is > very inefficient, especially if swap storage is fast. > 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. > 7. Alternative page reclaim policy to bias reclaiming anonymous page. > Currently reclaim anonymous page is considering harder than reclaim file pages, > so we bias reclaiming file pages. If there are high speed swap storage, we are > considering doing swap more aggressively. > 8. Huge page swap. Huge page swap can solve a lot of problems above, but both > THP and hugetlbfs don't support swap. > > I had some progresses in these areas recently: > http://marc.info/?l=linux-mm&m=134665691021172&w=2 > http://marc.info/?l=linux-mm&m=135336039115191&w=2 > http://marc.info/?l=linux-mm&m=135882182225444&w=2 > http://marc.info/?l=linux-mm&m=135754636926984&w=2 > http://marc.info/?l=linux-mm&m=135754634526979&w=2 > But a lot of problems remain. I'd like to discuss the issues at the meeting. > > Thanks, > Shaohua > > -- > 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> -- 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>