Messages in this thread | | | Date | Tue, 23 Oct 2007 11:30:35 +0200 | From | Andi Kleen <> | Subject | Re: [patch] Re: Interaction between Xen and XFS: stray RW mappings |
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On Tue, Oct 23, 2007 at 05:04:14PM +1000, David Chinner wrote: > On Tue, Oct 23, 2007 at 10:36:41AM +1000, David Chinner wrote: > > On Tue, Oct 23, 2007 at 01:35:14AM +0200, Andi Kleen wrote: > > > On Tue, Oct 23, 2007 at 08:32:25AM +1000, David Chinner wrote: > > > > Could vmap()/vunmap() take references to the pages that are mapped? That > > > > way delaying the unmap would also delay the freeing of the pages and hence > > > > we'd have no problems with the pages being reused before the mapping is > > > > torn down. That'd work for Xen even with XFS's lazy unmapping scheme, and > > > > would allow Nick's more advanced methods to work as well.... > > > > > > You could always just keep around an array of the pages and then drop the > > > reference count after unmap. Or walk the vmalloc mapping and generate such > > > an array before freeing, then unmap and then drop the reference counts. > > > > You mean like vmap() could record the pages passed to it in the area->pages > > array, and we walk and release than in __vunmap() like it already does > > for vfree()? > > > > If we did this, it would probably be best to pass a page release function > > into the vmap or vunmap call - we'd need page_cache_release() called on > > the page rather than __free_page().... > > > > The solution belongs behind the vmap/vunmap interface, not in XFS.... > > Lightly tested(*) patch that does this with lazy unmapping > below for comment.
Thanks
> > (*) a) kernel boots, b) made an XFS filesystem with 64k directory > blocks, created ~100,000 files in a directory to get a wide btree > (~1700 blocks, still only a single level) and run repeated finds > across it dropping caches in between. Each traversal maps and > unmaps every btree block.
Hmm, the __free_page -> page_cache_release() change in vfree() would have been simpler wouldn't it?
But if it works it is fine.
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