Messages in this thread | | | Date | Sat, 14 Jan 2006 07:04:24 +0000 (GMT) | From | Hugh Dickins <> | Subject | Re: [Patch] Add tmpfs options for memory placement policies (Resend with corrected addresses). |
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On Fri, 13 Jan 2006, Brent Casavant wrote: > On Fri, 13 Jan 2006, Andrew Morton wrote: > > > Confused. Is this for applications which cannot be taught to use the > > mempolicy API? > > In general yes. Anything that writes into a tmpfs filesystem is liable > to disproportionately decrease the available memory on a particular node. > Since there's no telling what sort of application (e.g. dd/cp/cat) might be > dropping large files there, this lets the admin choose the appropriate > default behavior for their site's situation.
I look at it differently, and would answer Andrew's question with "no" rather than "yes". The mempolicy API applies only to userspace mappings: so it covers shared memory fine, but cannot be applied to tmpfs files. Whereas mount's mpol= applies to tmpfs files, and (unfortunately?) cannot be applied to shm (since that's on an internal mount with no options).
The only overlap comes when a tmpfs file is mmap'ed: then it's possible to apply the mempolicy API to it, and refine what mount's mpol= defined. There's been talk in the past of mempolicy for pagecache, which would also allow mount's mpol= to be refined per file; but that's not appeared.
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