Messages in this thread | | | Subject | Re: [PATCH V2 0/6] VA to numa node information | From | "prakash.sangappa" <> | Date | Thu, 13 Sep 2018 15:32:25 -0700 |
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On 09/13/2018 01:40 AM, Michal Hocko wrote: > 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
The proc interface provides an efficient way to export address range to numa node id mapping information compared to using the API. For example, for sparsely populated mappings, if a VMA has large portions not have any physical pages mapped, the page walk done thru the /proc file interface can skip over non existent PMDs / ptes. Whereas using the API the application would have to scan the entire VMA in page size units.
Also, VMAs having THP pages can have a mix of 4k pages and hugepages. The page walks would be efficient in scanning and determining if it is a THP huge page and step over it. Whereas using the API, the application would not know what page size mapping is used for a given VA and so would have to again scan the VMA in units of 4k page size.
If this sounds reasonable, I can add it to the commit / patch description.
-Prakash.
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