On 08/21/2013 05:24 PM, Bob Liu wrote: > Hi Minchan, > > On 08/21/2013 02:16 PM, Minchan Kim wrote: >> It's 7th trial of zram/zsmalloc promotion. >> I rewrote cover-letter totally based on previous discussion. >> >> The main reason to prevent zram promotion was no review of >> zsmalloc part while Jens, block maintainer, already acked >> zram part. >> >> At that time, zsmalloc was used for zram, zcache and zswap so >> everybody wanted to make it general and at last, Mel reviewed it >> when zswap was submitted to merge mainline a few month ago. >> Most of review was related to zswap writeback mechanism which >> can pageout compressed page in memory into real swap storage >> in runtime and the conclusion was that zsmalloc isn't good for >> zswap writeback so zswap borrowed zbud allocator from zcache to >> replace zsmalloc. The zbud is bad for memory compression ratio(2) >> but it's very predictable behavior because we can expect a zpage >> includes just two pages as maximum. Other reviews were not major. >> http://lkml.indiana.edu/hypermail/linux/kernel/1304.1/04334.html >> >> Zcache doesn't use zsmalloc either so zsmalloc's user is only >> zram now so this patchset moves it into zsmalloc directory. >> Recently, Bob tried to move zsmalloc under mm directory to unify >> zram and zswap with adding pseudo block device in zswap(It's >> very weired to me) but he was simple ignoring zram's block device >> (a.k.a zram-blk) feature and considered only swap usecase of zram, >> in turn, it lose zram's good concept. >> > > Yes, I didn't notice the feature that zram can be used as a normal block > device. > > >> Mel raised an another issue in v6, "maintainance headache". >> He claimed zswap and zram has a similar goal that is to compresss >> swap pages so if we promote zram, maintainance headache happens >> sometime by diverging implementaion between zswap and zram >> so that he want to unify zram and zswap. For it, he want zswap >> to implement pseudo block device like Bob did to emulate zram so >> zswap can have an advantage of writeback as well as zram's benefit. > > If consider zram as a swap device only, I still think it's better to add > a pseudo block device to zswap and just disable the writeback of zswap. > > But I have no idea of zram's block device feature. > BTW: I think the original/main purpose that zram was introduced is for swapping. Is there any real users using zram as a normal block device instead of swap? For normal usage, maybe we can extend ramdisk with compression feature. -- 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>