Re: [PATCH v3 1/2] mm: introduce process_mrelease system call

[David Hildenbrand]

On 23.07.21 10:11, Suren Baghdasaryan wrote:
> On Thu, Jul 22, 2021, 11:20 PM Michal Hocko <mhocko@xxxxxxxx 
> <mailto:mhocko@xxxxxxxx>> wrote:
>
>     On Thu 22-07-21 21:47:56, Suren Baghdasaryan wrote:
>      > On Thu, Jul 22, 2021, 7:04 PM Shakeel Butt <shakeelb@xxxxxxxxxx
>     <mailto:shakeelb@xxxxxxxxxx>> wrote:
>      >
>      > > On Thu, Jul 22, 2021 at 6:14 PM Suren Baghdasaryan
>     <surenb@xxxxxxxxxx <mailto:surenb@xxxxxxxxxx>>
>      > > wrote:
>      > > >
>      > > [...]
>      > > > +
>      > > > +       mmap_read_lock(mm);
>      > >
>      > > How about mmap_read_trylock(mm) and return -EAGAIN on failure?
>      > >
>      >
>      > That sounds like a good idea. Thanks! I'll add that in the next
>     respin.
>
>     Why is that a good idea? Can you do anything meaningful about the
>     failure other than immediately retry the syscall and hope for the best?
>
>
> I was thinking if this syscall implements "best effort without blocking" 
> approach then for a more strict usage user can simply retry. However 
> retrying means issuing another syscall, so additional overhead...
> I guess such "best effort" approach would be unusual for a syscall, so 
> maybe we can keep it as it is now and if such "do not block" mode is 
> needed we can use flags to implement it later?

The process is dying, so I am not sure what we are trying to optimize 
here in respect to locking ...


--
Thanks,

David / dhildenb