linux-kernel - Re: [PATCH V2 0/6] VA to numa node information

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Message-ID: <20180913084011.GC20287@dhcp22.suse.cz>
Date:   Thu, 13 Sep 2018 10:40:11 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Prakash Sangappa <prakash.sangappa@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        dave.hansen@...el.com, nao.horiguchi@...il.com,
        akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        khandual@...ux.vnet.ibm.com, steven.sistare@...cle.com
Subject: Re: [PATCH V2 0/6] VA to numa node information

On Wed 12-09-18 13:23:58, Prakash Sangappa wrote:
> For analysis purpose it is useful to have numa node information
> corresponding mapped virtual address ranges of a process. Currently,
> the file /proc/<pid>/numa_maps provides list of numa nodes from where pages
> are allocated per VMA of a process. This is not useful if an user needs to
> determine which numa node the mapped pages are allocated from for a
> particular address range. It would have helped if the numa node information
> presented in /proc/<pid>/numa_maps was broken down by VA ranges showing the
> exact numa node from where the pages have been allocated.
> 
> The format of /proc/<pid>/numa_maps file content is dependent on
> /proc/<pid>/maps file content as mentioned in the manpage. i.e one line
> entry for every VMA corresponding to entries in /proc/<pids>/maps file.
> Therefore changing the output of /proc/<pid>/numa_maps may not be possible.
> 
> This patch set introduces the file /proc/<pid>/numa_vamaps which
> will provide proper break down of VA ranges by numa node id from where the
> mapped pages are allocated. For Address ranges not having any pages mapped,
> a '-' is printed instead of numa node id.
> 
> Includes support to lseek, allowing seeking to a specific process Virtual
> address(VA) starting from where the address range to numa node information
> can to be read from this file.
> 
> The new file /proc/<pid>/numa_vamaps will be governed by ptrace access
> mode PTRACE_MODE_READ_REALCREDS.
> 
> See following for previous discussion about this proposal
> 
> https://marc.info/?t=152524073400001&r=1&w=2

It would be really great to give a short summary of the previous
discussion. E.g. why do we need a proc interface in the first place when
we already have an API to query for the information you are proposing to
export [1]

[1] http://lkml.kernel.org/r/20180503085741.GD4535@dhcp22.suse.cz
-- 
Michal Hocko
SUSE Labs