Hi Sergey, On Mon, Oct 14, 2019 at 12:35 PM Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx> wrote: > > Hi, > > On (10/10/19 23:04), Vitaly Wool wrote: > [..] > > The coming patchset is a new take on the old issue: ZRAM can > > currently be used only with zsmalloc even though this may not > > be the optimal combination for some configurations. The previous > > (unsuccessful) attempt dates back to 2015 [1] and is notable for > > the heated discussions it has caused. > > Oh, right, I do recall it. > > > The patchset in [1] had basically the only goal of enabling > > ZRAM/zbud combo which had a very narrow use case. Things have > > changed substantially since then, and now, with z3fold used > > widely as a zswap backend, I, as the z3fold maintainer, am > > getting requests to re-interate on making it possible to use > > ZRAM with any zpool-compatible backend, first of all z3fold. > > A quick question, what are the technical reasons to prefer > allocator X over zsmalloc? Some data would help, I guess. For z3fold, the data can be found here: https://elinux.org/images/d/d3/Z3fold.pdf. For zbud (which is also of interest), imagine a low-end platform with a simplistic HW compressor that doesn't give really high ratio. We still want to be able to use ZRAM (not necessarily as a swap partition, but rather for /home and /var) but we absolutely don't need zsmalloc's complexity. zbud is a perfect match here (provided that it can cope with PAGE_SIZE pages, yes, but it's a small patch to make that work) since it's unlikely that we squeeze more than 2 compressed pages per page with that HW compressor anyway. > > The preliminary results for this work have been delivered at > > Linux Plumbers this year [2]. The talk at LPC, though having > > attracted limited interest, ended in a consensus to continue > > the work and pursue the goal of decoupling ZRAM from zsmalloc. > > [..] > > > [1] https://lkml.org/lkml/2015/9/14/356 > > I need to re-read it, thanks for the link. IIRC, but maybe > I'm wrong, one of the things Minchan was not happy with was > increased maintenance cost. So, perhaps, this also should > be discuss/addressed (and maybe even in the first place). I have hard time seeing how maintenance cost is increased here :) ~Vitaly
