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Subject: Re: [PATCH v3 1/2] mm: introduce process_mrelease system call
To:     Suren Baghdasaryan <surenb@google.com>,
        Michal Hocko <mhocko@suse.com>
Cc:     Shakeel Butt <shakeelb@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Rientjes <rientjes@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Roman Gushchin <guro@fb.com>, Rik van Riel <riel@surriel.com>,
        Minchan Kim <minchan@kernel.org>,
        Christian Brauner <christian@brauner.io>,
        Christoph Hellwig <hch@infradead.org>,
        Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Florian Weimer <fweimer@redhat.com>,
        Jan Engelhardt <jengelh@inai.de>,
        Tim Murray <timmurray@google.com>,
        Linux API <linux-api@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        kernel-team <kernel-team@android.com>
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From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <23ed1d8d-fe55-fdbc-ca33-01a3ce392dff@redhat.com>
Date:   Fri, 23 Jul 2021 10:15:30 +0200
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On 23.07.21 10:11, Suren Baghdasaryan wrote:
> 
> 
> On Thu, Jul 22, 2021, 11:20 PM Michal Hocko <mhocko@suse.com 
> <mailto:mhocko@suse.com>> wrote:
> 
>     On Thu 22-07-21 21:47:56, Suren Baghdasaryan wrote:
>      > On Thu, Jul 22, 2021, 7:04 PM Shakeel Butt <shakeelb@google.com
>     <mailto:shakeelb@google.com>> wrote:
>      >
>      > > On Thu, Jul 22, 2021 at 6:14 PM Suren Baghdasaryan
>     <surenb@google.com <mailto:surenb@google.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