Re: [PATCH] mm, memory_hotplug: Fix the wrong usage of N_HIGH_MEMORY

[Michal Hocko]

On Wed 20-03-19 17:06:24, Baoquan He wrote:
> On 03/20/19 at 09:46am, Michal Hocko wrote:
> > On Wed 20-03-19 16:07:32, Baoquan He wrote:
> > > In function node_states_check_changes_online(), N_HIGH_MEMORY is used
> > > to substitute ZONE_HIGHMEM directly. This is not right. N_HIGH_MEMORY
> > > always has value '3' if CONFIG_HIGHMEM=y, while ZONE_HIGHMEM's value
> > > is not. It depends on whether CONFIG_ZONE_DMA/CONFIG_ZONE_DMA32 are
> > > enabled. Obviously it's not true for CONFIG_ZONE_DMA32 on 32bit system,
> > > and CONFIG_ZONE_DMA is also optional.
> > > 
> > > Replace it with ZONE_HIGHMEM.
> > 
> > N*MEMORY is confusing as hell but I am really curious whether we have
> > ZONE_DMA32 and ZONE_HIGMEM together?
> 
> Not sure. AFAIK, on x86_32 it can't be.
> 
> > 
> > That being said N.*MEMORY is intended to check for nodes rather than
> > zones so the patch looks good to me but I think the above explanation is
> > misleading and will add even more mud to the picture when somebody tries
> > to understand what the heck is going on here.
> 
> Yes, agree. I also thought this again after I sent out patch, feel log is not
> good. As you said, they are value of enum node_states and enum zone_type
> separately.
> 
> How about this:
> 
> ~~~
> In function node_states_check_changes_online(), N_HIGH_MEMORY is used
> to substitute ZONE_HIGHMEM directly. This is not right. N_HIGH_MEMORY
> is to mark the memory state of node. Here zone index is checked, which
> should be compared with 'ZONE_HIGHMEM' accordingly.
> 
> Replace it with ZONE_HIGHMEM.

OK, this is better. Thanks!

Feel free to stamp the patch with
Acked-by: Michal Hocko <mhocko@xxxxxxxx>

-- 
Michal Hocko
SUSE Labs