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From:   Pintu Agarwal <pintu.ping@gmail.com>
Date:   Thu, 6 Jan 2022 22:19:55 +0530
Message-ID: <CAOuPNLifYFPU4Gt2+1sOSsYNNLQq7U2aGVaYknrhaMc-CVx8vg@mail.gmail.com>
Subject: Re: [PATCH] sysinfo: include availram field in sysinfo struct
To:     Cyrill Gorcunov <gorcunov@gmail.com>
Cc:     Pintu Kumar <quic_pintu@quicinc.com>,
        open list <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-mm <linux-mm@kvack.org>, ebiederm@xmission.com,
        christian.brauner@ubuntu.com, sfr@canb.auug.org.au,
        legion@kernel.org, sashal@kernel.org, chris.hyser@oracle.com,
        ccross@google.com, pcc@google.com, dave@stgolabs.net,
        caoxiaofeng@yulong.com, david@redhat.com
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On Thu, 6 Jan 2022 at 21:41, Cyrill Gorcunov <gorcunov@gmail.com> wrote:
>
> On Thu, Jan 06, 2022 at 09:04:10PM +0530, Pintu Kumar wrote:
> > The sysinfo member does not have any "available ram" field and
> > the bufferram field is not much helpful either, to get a rough
> > estimate of available ram needed for allocation.
> >
> > One needs to parse MemAvailable field separately from /proc/meminfo
> > to get this info instead of directly getting if from sysinfo itself.
> >
> > Thus, this patch introduce a new field as availram in sysinfo
> > so that all the info total/free/available can be retrieved from
> > one place itself.
> >
> > There are couple of places in kernel as well where this can be improved.
> > For example:
> > In fs/proc/meminfo.c:
> > meminfo_proc_show:
> >    si_meminfo(&i);
> >    available = si_mem_available();
> > Now with this change the second call be avoided.
> > Thus, we can directly do:
> > show_val_kb(m, "MemAvailable:   ", i.availram);
> >
> > Note, this also requires update in procfs for free and other commands.
> > Like in free command as well we frist call sysinfo then again parse
> > /proc/meminfo to get available field.
> > This can be avoided too with higher kernel version.
> >
> > A sample output with single sysinfo call is shown below:
> > Total RAM: 248376 kB
> >  Free RAM: 231540 kB
> > Avail RAM: 230448 kB
> >
> > Signed-off-by: Pintu Kumar <quic_pintu@quicinc.com>
> > Signed-off-by: Pintu Agarwal <pintu.ping@gmail.com>
> > ---
> >  include/uapi/linux/sysinfo.h | 1 +
> >  kernel/sys.c                 | 4 ++++
> >  mm/page_alloc.c              | 2 ++
> >  3 files changed, 7 insertions(+)
> >
> > diff --git a/include/uapi/linux/sysinfo.h b/include/uapi/linux/sysinfo.h
> > index 435d5c2..6e77e90 100644
> > --- a/include/uapi/linux/sysinfo.h
> > +++ b/include/uapi/linux/sysinfo.h
> > @@ -12,6 +12,7 @@ struct sysinfo {
> >       __kernel_ulong_t freeram;       /* Available memory size */
> >       __kernel_ulong_t sharedram;     /* Amount of shared memory */
> >       __kernel_ulong_t bufferram;     /* Memory used by buffers */
> > +     __kernel_ulong_t availram;      /* Memory available for allocation */
> >       __kernel_ulong_t totalswap;     /* Total swap space size */
> >       __kernel_ulong_t freeswap;      /* swap space still available */
> >       __u16 procs;                    /* Number of current processes */
>
> Hi! Sorry, but I don't understand -- the sysinfo structure seems to
> be part of user API, no? Don't we break it up here?

Yes, the corresponding user space header /usr/include/linux/sysinfo.h
also needs to be updated.
When we generate the kernel header it will be updated automatically.