Messages in this thread | | | Date | Fri, 22 Oct 2004 01:20:59 +0200 | From | Andrea Arcangeli <> | Subject | Re: [PATCH] zap_pte_range should not mark non-uptodate pages dirty |
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On Thu, Oct 21, 2004 at 04:02:33PM -0700, Andrew Morton wrote: > Andrea Arcangeli <andrea@novell.com> wrote: > > > > On Thu, Oct 21, 2004 at 02:45:31PM -0700, Andrew Morton wrote: > > > Maybe we should revisit invalidate_inode_pages2(). It used to be an > > > invariant that "pages which are mapped into process address space are > > > always uptodate". We broke that (good) invariant and we're now seeing > > > some fallout. There may be more. > > > > such invariant doesn't exists since 2.4.10. There's no way to get mmaps > > reload data from disk without breaking such an invariant. > > There are at least two ways: > > a) Set a new page flag in invalidate, test+clear that at fault time
What's the point of adding a new page flag when the invariant !PageUptodate && page_mapcount(page) already provides the information?
I turned a condition that previously was impossible, and it made such condition useful as another useful invariant, instead of a BUG_ON invariant. The BUG itself guarantees us nobody was using it for other purposes, infact invalidate_inode_pages2 is what triggered this in the first place.
> b) shoot down all pte's mapping the locked page at invalidate time, mark the > page not uptodate.
invalidate should run fast, I didn't enforce coherency or it'd hurt too much the O_DIRECT write if something is mapped, we only allow buffered read against O_DIRECT write to work coherently, the mmap coherency has never been provided to avoid having to search for vmas in the prio_tree for every single write to an inode.
> The latter is complex but has the advantage of fixing the current > half-assed situation wherein existing mmaps are seeing invalidated data.
that's a feature not a bug since 2.4.10. Nobody ever asked for such coherency, all we provide is read against write or read against read (write against write only with both writes O_DIRECT or both writes buffered). mmaps are ignored by O_DIRECT, mmaps don't crash the kernel (well modulo the PageReserved check added in 2.6) but that's all.
> We could just remove the BUG in mpage_writepage() (which I assume is the > one which was being hit) but we might still have a not uptodate page with > uptodate buffers and I suspect that the kernel will either go BUG there > instead or will bring the page uptodate again without performing any I/O. > But I haven't checked that.
how can this be related to mmapped pages? Isn't this only an issue with invalidate_inode_pages2? I agree we miss an invalidate of the bh there. the mpage_readpage not using bh coupled with the page-size alignment enforced by the 2.4 O_DIRECT API (not like 2.6 that uses hardblocksize alignment) probably helps a lot in hiding this I guess. - 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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