Messages in this thread | | | Date | Sat, 17 Apr 2004 00:10:09 +0100 | From | Jamie Lokier <> | Subject | Re: msync() needed before munmap() when writing to shared mapping? |
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Andrew Morton wrote: > Jamie Lokier <jamie@shareable.org> wrote: > > I've followed the logic from do_munmap() and it looks good: > > unmap_vmas->zap_pte_range->page_remove_rmap->set_page_dirty. > > > > Can someone confirm this is correct, please? > > yup, zap_pte_range() transfers pte dirtiness into pagecache dirtiness when > tearing down the mapping, leaving the dirty page floating about in > pagecache for kupdate/kswapd/fsync to catch. Longstanding behaviour.
Thanks.
A related question. The comment for MADV_DONTNEED says:
* NB: This interface discards data rather than pushes it out to swap, * as some implementations do. This has performance implications for * applications like large transactional databases which want to discard * pages in anonymous maps after committing to backing store the data * that was kept in them. There is no reason to write this data out to * the swap area if the application is discarding it. * * An interface that causes the system to free clean pages and flush * dirty pages is already available as msync(MS_INVALIDATE).
MADV_DONTNEED calls zap_page_range(). That propagates dirtiness into the pagecache.
So it *doesn't* "discard data rather than push it out to swap", if the same dirty data is mapped elsewhere e.g. as a shared anonymous mapping, does it?
The comment also mentions MS_INVALIDATE, but MS_INVALIDATE doesn't do what the comment says and doesn't implement anything like POSIX either. (Linux's MS_INVALIDATE is practically equivalent to MS_ASYNC).
Is there a call which does what the command about MS_INVALIDATE says, i.e. free clean pages and flush dirty ones?
Thanks, -- Jamie - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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