Messages in this thread | | | Date | Thu, 29 Jun 2017 17:47:26 +0900 | From | Minchan Kim <> | Subject | Re: [PATCH v1 0/7] writeback incompressible pages to storage |
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Hi Sergey,
On Thu, Jun 29, 2017 at 12:41:57AM +0900, Sergey Senozhatsky wrote: > Hello, > > On (06/26/17 15:52), Minchan Kim wrote: > [..] > > zRam is useful for memory saving with compressible pages but sometime, > > workload can be changed and system has lots of incompressible pages > > which is very harmful for zram. > > could do. that makes zram quite complicated, to be honest. no offense, > but the whole zram's "good compression" margin looks to me completely > random and quite unreasonable. building a complex logic atop of random > logic is a bit tricky. but I see what problem you are trying to address. > > > This patch supports writeback feature of zram so admin can set up > > a block device and with it, zram can save the memory via writing > > out the incompressile pages once it found it's incompressible pages > > (1/4 comp ratio) instead of keeping the page in memory. > > hm, alternative idea. just an idea. can we try compressing the page > with another algorithm? example: downcast from lz4 to zlib? we can > set up a fallback "worst case" algorithm, so each entry can contain > additional flag that would tell if the src page was compressed with > the fast or slow algorithm. that sounds to me easier than "create a > new block device and bond it to zram, etc". but I may be wrong.
We tried it although it was static not dynamic adatation you suggested. However problem was media-stream data so zlib, lzam added just pointless overhead.
Thanks.
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