Messages in this thread |  | | | Date | Tue, 17 Apr 2012 11:18:56 +0900 | | From | Minchan Kim <> | | Subject | Re: swap on eMMC and other flash |
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On 04/17/2012 06:12 AM, Stephan Uphoff wrote: > Hi Arnd, > > On Mon, Apr 16, 2012 at 12:59 PM, Arnd Bergmann<arnd@arndb.de> wrote: >> On Monday 16 April 2012, Stephan Uphoff wrote: >>> opportunity to plant a few ideas. >>> >>> In contrast to rotational disks read/write operation overhead and >>> costs are not symmetric. >>> While random reads are much faster on flash - the number of write >>> operations is limited by wearout and garbage collection overhead. >>> To further improve swapping on eMMC or similar flash media I believe >>> that the following issues need to be addressed: >>> >>> 1) Limit average write bandwidth to eMMC to a configurable level to >>> guarantee a minimum device lifetime >>> 2) Aim for a low write amplification factor to maximize useable write bandwidth >>> 3) Strongly favor read over write operations >>> >>> Lowering write amplification (2) has been discussed in this email >>> thread - and the only observation I would like to add is that >>> over-provisioning the internal swap space compared to the exported >>> swap space significantly can guarantee a lower write amplification >>> factor with the indirection and GC techniques discussed. >> >> Yes, good point. >> >>> I believe the swap functionality is currently optimized for storage >>> media where read and write costs are nearly identical. >>> As this is not the case on flash I propose splitting the anonymous >>> inactive queue (at least conceptually) - keeping clean anonymous pages >>> with swap slots on a separate queue as the cost of swapping them >>> out/in is only an inexpensive read operation. A variable similar to >>> swapiness (or a more dynamic algorithmn) could determine the >>> preference for swapping out clean pages or dirty pages. ( A similar >>> argument could be made for splitting up the file inactive queue ) >> >> I'm not sure I understand yet how this would be different from swappiness. > > As I see it swappiness determines the ratio for paging out file backed > as compared to anonymous, swap backed pages. > I would like to further be able to set the ratio for throwing away > clean anonymous pages with swap slots ( that are easy to read back in) > as compared to writing out dirty anonymous pages to swap.
We can apply the rule in file-lru list too and we already have ISOLATE_CLEAN mode to select victim pages in LRU list so it should work.
For selecting clean anon pages with swap slot, we need more looking. Recent, Dan had a question about it and Hugh answered it. Look at the http://marc.info/?l=linux-mm&m=133462346928786&w=2
-- Kind regards, Minchan Kim
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