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    SubjectRe: [PATCH] [13/16] HWPOISON: The high level memory error handler in the VM v3
    On Tue, Jun 02, 2009 at 03:25:38PM +0200, Andi Kleen wrote:
    > On Tue, Jun 02, 2009 at 02:57:13PM +0200, Nick Piggin wrote:
    > > > > not a big deal and just avoids duplicating code. I attached an
    > > > > (untested) patch.
    > > >
    > > > Thanks. But the function in the patch is not doing the same what
    > > > the me_pagecache_clean/dirty are doing. For once there is no error
    > > > checking, as in the second try_to_release_page()
    > > >
    > > > Then it doesn't do all the IO error and missing mapping handling.
    > >
    > > Obviously I don't mean just use that single call for the entire
    > > handler. You can set the EIO bit or whatever you like. The
    > > "error handling" you have there also seems strange. You could
    > > retain it, but the page is assured to be removed from pagecache.
    >
    > The reason this code double checks is that someone could have
    > a reference (remember we can come in any time) we cannot kill immediately.

    Can't kill what? The page is gone from pagecache. It may remain
    other kernel references, but I don't see why this code will
    consider this as a failure (and not, for example, a raised error
    count).


    > > > The page_mapped() check is useless because the pages are not
    > > > mapped here etc.
    > >
    > > That's OK, it is a core part of the protocol to prevent
    > > truncated pages from being mapped, so I like it to be in
    > > that function.
    > >
    > > (you are also doing extraneous page_mapped tests in your handler,
    > > so surely your concern isn't from the perspective of this
    > > error handler code)
    >
    > We do page_mapping() checks, not page_mapped checks.
    >
    > I know details, but ...

    +static int me_pagecache_clean(struct page *p)
    +{
    + if (!isolate_lru_page(p))
    + page_cache_release(p);
    +
    + if (page_has_private(p))
    + do_invalidatepage(p, 0);
    + if (page_has_private(p) && !try_to_release_page(p, GFP_NOIO))
    + Dprintk(KERN_ERR "MCE %#lx: failed to release buffers\n",
    + page_to_pfn(p));
    +
    + /*
    + * remove_from_page_cache assumes (mapping && !mapped)
    + */
    + if (page_mapping(p) && !page_mapped(p)) {
    ^^^^^^^^^^^^^^^

    + remove_from_page_cache(p);
    + page_cache_release(p);
    + }
    +
    + return RECOVERED;


    > > > we would also need to duplicate most of the checking outside
    > > > the function anyways and there wouldn't be any possibility
    > > > to share the clean/dirty variants. If you insist I can
    > > > do it, but I think it would be significantly worse code
    > > > than before and I'm reluctant to do that.
    > >
    > > I can write you the patch for that too if you like.
    >
    > Ok I will write it, but I will add a comment saying that Nick forced
    > me to make the code worse @)
    >
    > It'll be fairly redundant at least.

    If it's that bad, then I'll be happy to rewrite it for you.


    > > > > if you already have other large ones.
    > > >
    > > > That's unclear too.
    > >
    > > You can't do much about most kernel pages, and dirty metadata pages
    > > are both going to cause big problems. User pagetable pages. Lots of
    > > stuff.
    >
    > User page tables was on the todo list, these are actually relatively
    > easy. The biggest issue is to detect them.
    >
    > Metadata would likely need file system callbacks, which I would like to
    > avoid at this point.

    So I just don't know why you argue the point that you have lots
    of large holes left.


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