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 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>
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