lkml.org 
[lkml]   [2023]   [Jan]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 2/3] mm/mprotect: Use long for page accountings and retval
From
On 04.01.23 23:52, Peter Xu wrote:
> Switch to use type "long" for page accountings and retval across the whole
> procedure of change_protection().
>
> The change should have shrinked the possible maximum page number to be half
> comparing to previous (ULONG_MAX / 2), but it shouldn't overflow on any
> system either because the maximum possible pages touched by change
> protection should be ULONG_MAX / PAGE_SIZE.

Yeah, highly unlikely.

>
> Two reasons to switch from "unsigned long" to "long":
>
> 1. It suites better on count_vm_numa_events(), whose 2nd parameter takes
> a long type.
>
> 2. It paves way for returning negative (error) values in the future.
>
> Currently the only caller that consumes this retval is change_prot_numa(),
> where the unsigned long was converted to an int. Since at it, touching up
> the numa code to also take a long, so it'll avoid any possible overflow too
> during the int-size convertion.

I'm wondering if we should just return the number of changed pages via a
separate pointer and later using an int for returning errors -- when
touching this interface already.

Only who's actually interested in the number of pages would pass a
pointer to an unsigned long (NUMA).

And code that expects that there never ever are failures (mprotect,
NUMA) could simply check for WARN_ON_ONCE(ret).

I assume you evaluated that option as well, what was your conclusion?

--
Thanks,

David / dhildenb

\
 
 \ /
  Last update: 2023-03-26 23:28    [W:0.229 / U:0.032 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site