linux-kernel - Re: [PATCH v3 2/2] Documentation/filesystems/proc.txt: Add more description for maps/smaps

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Message-ID: <57E552F2.4030302@intel.com>
Date:   Fri, 23 Sep 2016 09:06:10 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Robert Ho <robert.hu@...el.com>, pbonzini@...hat.com,
        akpm@...ux-foundation.org, mhocko@...e.com, oleg@...hat.com,
        dan.j.williams@...el.com
Cc:     guangrong.xiao@...ux.intel.com, gleb@...nel.org,
        mtosatti@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stefanha@...hat.com,
        yuhuang@...hat.com, linux-mm@...ck.org,
        ross.zwisler@...ux.intel.com
Subject: Re: [PATCH v3 2/2] Documentation/filesystems/proc.txt: Add more
 description for maps/smaps

On 09/23/2016 06:12 AM, Robert Ho wrote:
> +Note: for both /proc/PID/maps and /proc/PID/smaps readings, it's
> +possible in race conditions, that the mappings printed may not be that
> +up-to-date, because during each read walking, the task's mappings may have
> +changed, this typically happens in multithread cases. But anyway in each single
> +read these can be guarunteed: 1) the mapped addresses doesn't go backward; 2) no
> +overlaps 3) if there is something at a given vaddr during the entirety of the
> +life of the smaps/maps walk, there will be some output for it.

Could we spuce this description up a bit?  Perhaps:

Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy.
This typically manifests when doing partial reads of these files while
the memory map is being modified.  Despite the races, we do provide the
following guarantees:
1) The mapped addresses never go backwards, which implies no two
   regions will ever overlap.
2) If there is something at a given vaddr during the entirety of the
   life of the smaps/maps walk, there will be some output for it.