linux-kernel - Re: [PATCH v3 1/2] mm: introduce process

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Date:   Fri, 23 Jul 2021 10:15:30 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Suren Baghdasaryan <surenb@...gle.com>,
        Michal Hocko <mhocko@...e.com>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, Rik van Riel <riel@...riel.com>,
        Minchan Kim <minchan@...nel.org>,
        Christian Brauner <christian@...uner.io>,
        Christoph Hellwig <hch@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Florian Weimer <fweimer@...hat.com>,
        Jan Engelhardt <jengelh@...i.de>,
        Tim Murray <timmurray@...gle.com>,
        Linux API <linux-api@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH v3 1/2] mm: introduce process_mrelease system call

On 23.07.21 10:11, Suren Baghdasaryan wrote:
> 
> 
> On Thu, Jul 22, 2021, 11:20 PM Michal Hocko <mhocko@...e.com 
> <mailto:mhocko@...e.com>> wrote:
> 
>     On Thu 22-07-21 21:47:56, Suren Baghdasaryan wrote:
>      > On Thu, Jul 22, 2021, 7:04 PM Shakeel Butt <shakeelb@...gle.com
>     <mailto:shakeelb@...gle.com>> wrote:
>      >
>      > > On Thu, Jul 22, 2021 at 6:14 PM Suren Baghdasaryan
>     <surenb@...gle.com <mailto:surenb@...gle.com>>
>      > > 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