Messages in this thread | | | Date | Thu, 15 Jan 2015 01:36:30 +0200 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH v2 2/2] task_mmu: Add user-space support for resetting mm->hiwater_rss (peak RSS) |
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On Wed, Jan 14, 2015 at 03:22:25PM +0000, Petr Cermak wrote: > On Wed, Jan 07, 2015 at 07:24:52PM +0200, Kirill A. Shutemov wrote: > > And how it's not an ABI break? > I don't think this is an ABI break because the current behaviour is not > changed unless you write "5" to /proc/pid/clear_refs. If you do, you are > explicitly requesting the new functionality.
I'm not sure if it should be considered ABI break or not. Just asking.
I would like to hear opinion from other people. > > We have never-lowering VmHWM for 9+ years. How can you know that nobody > > expects this behaviour? > This is why we sent an RFC [1] several weeks ago. We expect this to be > used mainly by performance-related tools (e.g. profilers) and from the > comments in the code [2] VmHWM seems to be a best-effort counter. If this > is strictly a no-go, I can only think of the following two alternatives: > > 1. Add an extra resettable field to /proc/pid/status (e.g. > resettable_hiwater_rss). While this doesn't violate the current > definition of VmHWM, it adds an extra line to /proc/pid/status, > which I think is a much bigger issue.
I don't think extra line is bigger issue. Sane applications would look for a key, not line number. We do add lines there. I've posted patch which adds one more just today ;)
> 2. Introduce a new proc fs file to task_mmu (e.g. > /proc/pid/profiler_stats), but this feels like overengineering. > > > And why do you reset hiwater_rss, but not hiwater_vm? > This is a good point. Should we reset both using the same flag, or > introduce a new one ("6")? > > [1] lkml.iu.edu/hypermail/linux/kernel/1412.1/01877.html > [2] task_mmu.c:32: "... such snapshots can always be inconsistent." -- Kirill A. Shutemov
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