linux-kernel - RE: [PATCH v2] sysinfo: include availram field in sysinfo struct

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Date:   Fri, 7 Jan 2022 22:22:21 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Pintu Kumar' <quic_pintu@...cinc.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "ebiederm@...ssion.com" <ebiederm@...ssion.com>,
        "christian.brauner@...ntu.com" <christian.brauner@...ntu.com>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "legion@...nel.org" <legion@...nel.org>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "gorcunov@...il.com" <gorcunov@...il.com>,
        "chris.hyser@...cle.com" <chris.hyser@...cle.com>,
        "ccross@...gle.com" <ccross@...gle.com>,
        "pcc@...gle.com" <pcc@...gle.com>,
        "dave@...olabs.net" <dave@...olabs.net>,
        "caoxiaofeng@...ong.com" <caoxiaofeng@...ong.com>,
        "david@...hat.com" <david@...hat.com>,
        "pintu.ping@...il.com" <pintu.ping@...il.com>,
        "vbabka@...e.cz" <vbabka@...e.cz>
CC:     "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: RE: [PATCH v2] sysinfo: include availram field in sysinfo struct

From: Pintu Kumar
> Sent: 07 January 2022 18:08
> 
> 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.
> 
...
> diff --git a/include/uapi/linux/sysinfo.h b/include/uapi/linux/sysinfo.h
> index 435d5c2..fe84c6a 100644
> --- a/include/uapi/linux/sysinfo.h
> +++ b/include/uapi/linux/sysinfo.h
> @@ -19,7 +19,8 @@ struct sysinfo {
>  	__kernel_ulong_t totalhigh;	/* Total high memory size */
>  	__kernel_ulong_t freehigh;	/* Available high memory size */
>  	__u32 mem_unit;			/* Memory unit size in bytes */
> -	char _f[20-2*sizeof(__kernel_ulong_t)-sizeof(__u32)];	/* Padding: libc5 uses this.. */

There are 4 pad bytes here on most 64bit architectures.

> +	__kernel_ulong_t availram;	/* Memory available for allocation */
> +	char _f[20-3*sizeof(__kernel_ulong_t)-sizeof(__u32)];	/* Padding: libc5 uses this.. */
>  };

You've not compile-time tested the size of the structure.

	David

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