Bug 435721 - mmap may keep mmap_sem for a long time
mmap may keep mmap_sem for a long time
Product: Red Hat Enterprise MRG
Classification: Red Hat
Component: realtime-kernel (Show other bugs)
i386 Linux
low Severity high
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Assigned To: Red Hat Real Time Maintenance
Depends On:
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Reported: 2008-03-03 10:27 EST by Roland Westrelin
Modified: 2012-01-05 16:06 EST (History)
3 users (show)

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Last Closed: 2012-01-05 16:06:26 EST
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Description Roland Westrelin 2008-03-03 10:27:37 EST
Description of problem:

If a process locks its virtual address space in physical memory (either with
mlockall() or with the MAP_LOCKED flag of mmap), the time a call to mmap takes
increases with the size of the requested mapping and can take up to several tens
or hundreds of milliseconds. The whole time, mmap_sem is kept by the thread that
is mmaping thus preventing any other thread that also requires the mmap_sem in
the process from making progress.

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Comment 1 Peter Zijlstra 2008-09-30 13:42:08 EDT
That is expected behaviour as the mmap call will have to install every page for such a mapping, therefore the time will increase linearly with the number of pages in it.

What other mmap_sem users in particular are held up by this?
Comment 2 Beth Uptagrafft 2009-09-22 16:03:04 EDT
There has been no recent activity on this issue. Is this still a problem?

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