Hi Seth, On Wed, Mar 27, 2013 at 12:19:11PM -0500, Seth Jennings wrote: > On 03/26/2013 09:22 PM, Minchan Kim wrote: > > Swap subsystem does lazy swap slot free with expecting the page > > would be swapped out again so we can't avoid unnecessary write. > > > > But the problem in in-memory swap is that it consumes memory space > > until vm_swap_full(ie, used half of all of swap device) condition > > meet. It could be bad if we use multiple swap device, small in-memory swap > > and big storage swap or in-memory swap alone. > > > > This patch changes vm_swap_full logic slightly so it could free > > swap slot early if the backed device is really fast. > > Great idea! Thanks! > > > For it, I used SWP_SOLIDSTATE but It might be controversial. > > The comment for SWP_SOLIDSTATE is that "blkdev seeks are cheap". Just > because seeks are cheap doesn't mean the read itself is also cheap. The "read" isn't not concern but "write". > For example, QUEUE_FLAG_NONROT is set for mmc devices, but some of > them can be pretty slow. Yeb. > > > So let's add Ccing Shaohua and Hugh. > > If it's a problem for SSD, I'd like to create new type SWP_INMEMORY > > or something for z* family. > > Afaict, setting SWP_SOLIDSTATE depends on characteristics of the > underlying block device (i.e. blk_queue_nonrot()). zram is a block > device but zcache and zswap are not. > > Any idea by what criteria SWP_INMEMORY would be set? Just in-memory swap, zram, zswap and zcache at the moment. :) > > Also, frontswap backends (zcache and zswap) are a caching layer on top > of the real swap device, which might actually be rotating media. So > you have the issue of to different characteristics, in-memory caching > on top of rotation media, present in a single swap device. Please read my patch completely. I already pointed out the problem and Hugh and Dan are suggesting ideas. Thanks! > > Thanks, > Seth > > -- > 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> -- Kind regards, Minchan Kim -- 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>