Messages in this thread | | | Subject | Re: [PATCHv3, RESEND 5/8] khugepaged: Allow to collapse a page shared across fork | From | John Hubbard <> | Date | Tue, 14 Apr 2020 19:42:39 -0700 |
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On 2020-04-14 14:35, Kirill A. Shutemov wrote: > 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. >
Yes, you are right. I misread the condition. This actually is just right. :)
thanks, -- John Hubbard NVIDIA
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