On Thu 16-11-23 11:30:04, Charan Teja Kalla wrote: > Thanks Michal. > > On 11/15/2023 7:39 PM, Michal Hocko wrote: > >> Also If you have any comments on [PATCH V2 2/3] mm: page_alloc: correct > >> high atomic reserve calculations will help me. > > I do not have a strong opinion on that one to be honest. I am not even > > sure that reserving a full page block (4MB) on small systems as > > presented is really a good use of memory. > > May be other way to look at that patch is comment is really not being > reflected in the code. It says, " Limit the number reserved to 1 > pageblock or roughly 1% of a zone.", but the current code is making it 2 > pageblocks. So, for 4M block size, it is > 1%. > > A second patch, that I will post, like not reserving the high atomic > page blocks on small systems -- But how to define the meaning of small > systems is not sure. Instead will let the system administrators chose > this through either: > a) command line param, high_atomic_reserves=off, on by default -- > Another knob, so admins may really not like this? > b) CONFIG_HIGH_ATOMIC_RESERVES, which if not defined, will not reserve. Please don't! I do not see any admin wanting to care about this at all. It just takes a lot of understanding of internal MM stuff to make an educated guess. This should really be auto-tuned. And as responded in other reply my take would be to reserve a page block on if it doesn't consume more than 1% of memory to preserve the existing behavior yet not overconsume on small systems. > Please lmk If you have any more suggestions here? > > Also, I am thinking to request Andrew to pick [PATCH V2 1/3] patch and > take these discussions separately in a separate thread. That makes sense as that is a clear bug fix. -- Michal Hocko SUSE Labs
