Messages in this thread | | | Date | Mon, 19 Apr 2004 16:01:34 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: Non-linear mappings and truncate/madvise(MADV_DONTNEED) |
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On Mon, 19 Apr 2004, Jamie Lokier wrote: > A couple of thoughts on non-linear mappings. Vanilla 2.6.5. > > I'm reading madvise_dontneed() and thinking about that zap_page_range() > call. It'll wipe non-linear file offset ptes, won't it?
Yes, at present.
> MADV_DONTNEED is actually a reasonable thing to do with a non-linear > mapping, when you no longer need some of the pages. You could argue > that losing the offsets is acceptable in this case, but I think it's a > poor argument. The offsets should be preserved while zapping the ptes.
Yes. And I think it also implies that the ->populate functions are wrong to fail beyond EOF, should just set up file ptes there.
> Then there's vmtruncate() and invalidate_mmap_range() which calls > zap_page_range(). When you call truncate(), the non-linear offsets > appear to be lost (I'm reading the code, not testing it) for the part > of each VMA corresponding to where the linear mapping would have been. > > That means (a) a peculiar part of the mapping is lost, and (b) some of > the truncated pages will stay mapped, if they're in a part of a VMA > which didn't get wiped by the linear calculation. > > Do any of the latest objrmap patches fix these problems? Have I > misdiagnosed these problems?
rmap 6 nonlinear truncation (which never appeared on LKML, though sent twice) fixed most of this, and went into 2.6.6-rc1-bk4 last night: please check it out.
But I just converted madvise_dontneed by rote, adding a NULL arg to zap_page_range, missing your point that it should respect nonlinearity.
And I made the zap_details structure private to mm/memory.c since I hadn't noticed anything outside needing it: I'll fix that up later and post a patch.
I'm haven't and don't intend to change the behaviour of ->populate, without agreement from others - Ingo? Jamie?
Hugh
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