RE: [External] Re: [RFC PATCH v2 00/12] get rid of GFP_ZONE_TABLE/BAD

[Huaisheng HS1 Ye]

From: owner-linux-mm@xxxxxxxxx [mailto:owner-linux-mm@xxxxxxxxx] On Behalf Of Michal Hocko
Sent: Monday, May 28, 2018 9:38 PM
> > In my opinion, originally there shouldn't be such many wrong
> > combinations of these bottom 3 bits. For any user, whether or
> > driver and fs, they should make a decision that which zone is they
> > preferred. Matthew's idea is great, because with it the user must
> > offer an unambiguous flag to gfp zone bits.
> 
> Well, I would argue that those shouldn't really care about any zones at
> all. All they should carea bout is whether they really need a low mem
> zone (aka directly accessible to the kernel), highmem or they are the
> allocation is generally movable. Mixing zones into the picture just
> makes the whole thing more complicated and error prone.

Dear Michal,

I don't quite understand that. I think those, mostly drivers, need to
get the correct zone they want. ZONE_DMA32 is an example, if drivers can be
satisfied with a low mem zone, why they mark the gfp flags as
'GFP_KERNEL|__GFP_DMA32'?
GFP_KERNEL is enough to make sure a directly accessible low mem, but it is
obvious that they want to get a DMA accessible zone below 4G.

> This should be a part of the changelog. Please note that you should
> provide some number if you claim performance benefits. The complexity
> will always be subjective.

Sure, I will post them to changelog with next version of patches.

Sincerely,
Huaisheng Ye