linux-kernel - Re: [PATCH v7 2/7] mm: introduce external memory hinting API

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Message-ID: <20200310222008.GB72963@google.com>
Date:   Tue, 10 Mar 2020 15:20:08 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, linux-api@...r.kernel.org,
        oleksandr@...hat.com, Suren Baghdasaryan <surenb@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Dias <joaodias@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Jann Horn <jannh@...gle.com>,
        alexander.h.duyck@...ux.intel.com, sj38.park@...il.com
Subject: Re: [PATCH v7 2/7] mm: introduce external memory hinting API

On Thu, Mar 05, 2020 at 07:15:10PM +0100, Vlastimil Babka wrote:
> On 3/2/20 8:36 PM, Minchan Kim wrote:
> > There is usecase that System Management Software(SMS) want to give
> > a memory hint like MADV_[COLD|PAGEEOUT] to other processes and
> > in the case of Android, it is the ActivityManagerService.
> > 
> > It's similar in spirit to madvise(MADV_WONTNEED), but the information
> 
> You mean MADV_DONTNEED?

Mean to DONT_NEED's future version.

> 
> > required to make the reclaim decision is not known to the app.
> 
> This seems to be mixing up the differences between MADV_DONTNEED and
> COLD/PAGEOUT and self-imposed vs external memory hints?

Sorry, I don't understand what you want here.

> 
> > Instead,
> > it is known to the centralized userspace daemon(ActivityManagerService),
> > and that daemon must be able to initiate reclaim on its own without
> > any app involvement.
> > 
> > To solve the issue, this patch introduces a new syscall process_madvise(2).
> > It uses pidfd of an external process to give the hint.
> > 
> >  int process_madvise(int pidfd, void *addr, size_t length, int advise,
> > 			unsigned long flag);
> 
> It's more common to call the argument 'flags' not 'flag'? The code seems to call
> it flags. Also in line with madvise(2), the 'advise' argument should rather be
> 'advice'. This is more important for the manpage, but let's be consistent.

Yub, I will send the patch along with your comment in previous patch.

> 
> ...
> 
> > 
> > Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
> > Signed-off-by: Minchan Kim <minchan@...nel.org>
> 
> For the core parts,
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

Thanks for the review!