Messages in this thread | | | Date | Wed, 15 Apr 2020 00:35:26 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCHv3, RESEND 5/8] khugepaged: Allow to collapse a page shared across fork |
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On Mon, Apr 13, 2020 at 01:48:22PM -0700, John Hubbard wrote:
[Thanks for all your suggestions and corrections]
> > + if (IS_ENABLED(CONFIG_DEBUG_VM) && expected_refcount > refcount) { > > + pr_err("expected_refcount: %d, refcount: %d\n", > > + expected_refcount, refcount); > > + dump_page(page, "Unexpected refcount"); > > > I see two issues with the pr_err() and the dump_page() call: > > 1. You probably want to rate limit this, otherwise you'll have a big > problem if lots of pages are pinned!
Nope. Only if kernel is buggy. See below.
> 2. Actually, I don't think you'd want to print anything at all here, even with > rate limiting, because doing so presumes that "unexpected" means "wrong". And I > think this patch doesn't expect to have GUP pins (or pin_user_pages() pins, ha), > but that doesn't mean that they're wrong to have.
See condition. We only do it if refcount is *below* expected refcount. It should never happen. Pinned page would have refcount above expected.
-- Kirill A. Shutemov
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