On Wed, Aug 08, 2018 at 04:02:29PM -0700, Shakeel Butt wrote: > On Wed, Aug 8, 2018 at 11:02 AM Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote: > > > > On Wed, Aug 08, 2018 at 07:30:13PM +0300, Kirill Tkhai wrote: > > > On 08.08.2018 19:23, Kirill Tkhai wrote: > > > > On 08.08.2018 19:13, Josh Triplett wrote: > > > >> On Wed, Aug 08, 2018 at 01:17:44PM +0300, Kirill Tkhai wrote: > > > >>> On 08.08.2018 10:20, Michal Hocko wrote: > > > >>>> On Tue 07-08-18 18:37:36, Kirill Tkhai wrote: > > > >>>>> This patch kills all CONFIG_SRCU defines and > > > >>>>> the code under !CONFIG_SRCU. > > > >>>> > > > >>>> The last time somebody tried to do this there was a pushback due to > > > >>>> kernel tinyfication. So this should really give some numbers about the > > > >>>> code size increase. Also why can't we make this depend on MMU. Is > > > >>>> anybody else than the reclaim asking for unconditional SRCU usage? > > > >>> > > > >>> I don't know one. The size numbers (sparc64) are: > > > >>> > > > >>> $ size image.srcu.disabled > > > >>> text data bss dec hex filename > > > >>> 5117546 8030506 1968104 15116156 e6a77c image.srcu.disabled > > > >>> $ size image.srcu.enabled > > > >>> text data bss dec hex filename > > > >>> 5126175 8064346 1968104 15158625 e74d61 image.srcu.enabled > > > >>> The difference is: 15158625-15116156 = 42469 ~41Kb > > > >> > > > >> 41k is a *substantial* size increase. However, can you compare > > > >> tinyconfig with and without this patch? That may have a smaller change. > > > > > > > > $ size image.srcu.disabled > > > > text data bss dec hex filename > > > > 1105900 195456 63232 1364588 14d26c image.srcu.disabled > > > > > > > > $ size image.srcu.enabled > > > > text data bss dec hex filename > > > > 1106960 195528 63232 1365720 14d6d8 image.srcu.enabled > > > > > > > > 1365720-1364588 = 1132 ~ 1Kb > > > > > > 1Kb is not huge size. It looks as not a big price for writing generic code > > > for only case (now some places have CONFIG_SRCU and !CONFIG_SRCU variants, > > > e.g. drivers/base/core.c). What do you think? > > > > That's a little more reasonable than 41k, likely because of > > CONFIG_TINY_SRCU. That's still not ideal, though. And as far as I can > > tell, the *only* two pieces of core code that use SRCU are > > drivers/base/core.c and kernel/notifier.c, and the latter is exclusively > > code to use notifiers with SRCU, not notifiers wanting to use SRCU > > themselves. So, as far as I can tell, this would really just save a > > couple of small #ifdef sections in drivers/base/core.c, and I think > > those #ifdef sections could be simplified even further. That doesn't > > seem worth it at all. > > Hi Josh, the motivation behind enabling SRCU is not to simplify the > code in drivers/base/core.c but rather not to introduce similar ifdefs > in mm/vmscan.c for shrinker traversals. Leaving aside the comment someone made about sticking with rwsem for this, I honestly hope that someday the shrinker is optional too. :)
