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. -- Regards, -Bob -- 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>