lkml.org 
[lkml]   [2018]   [Jun]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] mm: drop VM_BUG_ON from __get_free_pages
On Wed 27-06-18 12:47:39, Vlastimil Babka wrote:
> On 06/27/2018 09:54 AM, Michal Hocko wrote:
> > On Wed 27-06-18 09:50:01, Vlastimil Babka wrote:
> >> On 06/27/2018 09:34 AM, Michal Hocko wrote:
> >>> On Tue 26-06-18 10:04:16, Andrew Morton wrote:
> >>>
> >>> And as I've argued before the code would be wrong regardless. We would
> >>> leak the memory or worse touch somebody's else kmap without knowing
> >>> that. So we have a choice between a mem leak, data corruption k or a
> >>> silent fixup. I would prefer the last option. And blowing up on a BUG
> >>> is not much better on something that is easily fixable. I am not really
> >>> convinced that & ~__GFP_HIGHMEM is something to lose sleep over.
> >>
> >> Maybe put the fixup into a "#ifdef CONFIG_HIGHMEM" block and then modern
> >> systems won't care? In that case it could even be if (WARN_ON_ONCE(...))
> >> so future cases with wrong expectations would become known.
> >
> > Yes that could be done as well. Or maybe we can make __GFP_HIGHMEM 0 for
> > !HIGHMEM systems. Does something really rely on it being non-zero?
>
> I guess gfp_zone() would have to be checked, dunno about the rewrite of
> GFP_ZONE_TABLE (CCing people).
> In general checks like "if (flags & __GFP_HIGHMEM)" would become false,
> which probably should not be a problem, unless something expect the flag
> to be there and errors out if it isn't.

Well, __GFP_HIGHMEM should be basically GFP_KERNEL for !highmem systems.
But most checks I have seen try to mask it off. Having it 0 would help
to reduce at least some code.

--
Michal Hocko
SUSE Labs

\
 
 \ /
  Last update: 2018-06-27 13:06    [W:0.073 / U:0.364 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site