On Tue, Mar 19, 2013 at 09:27:25AM +0800, Shaohua Li wrote: >On Mon, Mar 18, 2013 at 06:38:29PM +0800, Bob Liu wrote: >> >> On 03/15/2013 05:39 PM, Simon Jeons wrote: >> > On 01/22/2013 02:53 PM, 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 >> >> 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. >> > >> > Could you tell me in which workload hugetlb/thp pages can't swapout >> > influence your performance? Is it worth? >> > >> >> I'm also very interesting in this workload. >> I think hugetlb/thp pages can be a potential user of zprojects like >> zswap/zcache. >> We can try to compress those pages before breaking them to normal pages. > >I don't have particular workload and don't have data for obvious reason. What I >expected is swapout hugetlb/thp is to reduce some overheads (eg, tlb flush) and >improve IO pattern. Hi Shaohua and Bob, I'm doing this work currently. :-) Regards, Wanpeng Li > >-- >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>