Hi Michal, On Wed, Mar 03, 2021 at 12:39:57PM +0100, Michal Hocko wrote: > On Wed 03-03-21 18:20:58, Feng Tang wrote: > > When doing broader test, we noticed allocation slowness in one test > > case that malloc memory with size which is slightly bigger than free > > memory of targeted nodes, but much less then the total free memory > > of system. > > > > The reason is the code enters the slowpath of __alloc_pages_nodemask(), > > which takes quite some time. As alloc_pages_policy() will give it a 2nd > > try with NULL nodemask, so there is no need to enter the slowpath for > > the first try. Add a new gfp bit to skip the slowpath, so that user cases > > like this can leverage. > > > > With it, the malloc in such case is much accelerated as it never enters > > the slowpath. > > > > Adding a new gfp_mask bit is generally not liked, and another idea is to > > add another nodemask to struct 'alloc_context', so it has 2: 'preferred-nmask' > > and 'fallback-nmask', and they will be tried in turn if not NULL, with > > it we can call __alloc_pages_nodemask() only once. > > Yes, it is very much disliked. Is there any reason why you cannot use > GFP_NOWAIT for that purpose? I did try that at the first place, but it didn't obviously change the slowness. I assumed the direct claim was still involved as GFP_NOWAIT only impact kswapd reclaim. Thanks, Feng > -- > Michal Hocko > SUSE Labs
