Date:   Thu, 6 Jan 2022 19:11:34 +0300
From:   Cyrill Gorcunov <gorcunov@gmail.com>
To:     Pintu Kumar <quic_pintu@quicinc.com>
Cc:     linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        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, pintu.ping@gmail.com
Subject: Re: [PATCH] sysinfo: include availram field in sysinfo struct
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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?