From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
akpm@linux-foundation.org, Andrea Arcangeli <aarcange@redhat.com>,
Zi Yan <ziy@nvidia.com>, Yang Shi <yang.shi@linux.alibaba.com>,
Ralph Campbell <rcampbell@nvidia.com>,
William Kucharski <william.kucharski@oracle.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCHv3, RESEND 5/8] khugepaged: Allow to collapse a page shared across fork
Date: Wed, 15 Apr 2020 00:35:26 +0300 [thread overview]
Message-ID: <20200414213526.ecn3zcgnqxoveddq@box> (raw)
In-Reply-To: <0efcc512-6f12-1ff0-9885-871172fac766@nvidia.com>
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
next prev parent reply other threads:[~2020-04-14 21:35 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-13 12:52 [PATCHv3, RESEND 0/8] thp/khugepaged improvements and CoW semantics Kirill A. Shutemov
2020-04-13 12:52 ` [PATCHv3, RESEND 1/8] khugepaged: Add self test Kirill A. Shutemov
2020-04-15 15:39 ` Zi Yan
2020-04-15 20:11 ` Yang Shi
2020-04-13 12:52 ` [PATCHv3, RESEND 2/8] khugepaged: Do not stop collapse if less than half PTEs are referenced Kirill A. Shutemov
2020-04-15 20:31 ` Yang Shi
2020-04-13 12:52 ` [PATCHv3, RESEND 3/8] khugepaged: Drain all LRU caches before scanning pages Kirill A. Shutemov
2020-04-15 20:31 ` Yang Shi
2020-04-13 12:52 ` [PATCHv3, RESEND 4/8] khugepaged: Drain LRU add pagevec after swapin Kirill A. Shutemov
2020-04-15 20:32 ` Yang Shi
2020-04-13 12:52 ` [PATCHv3, RESEND 5/8] khugepaged: Allow to collapse a page shared across fork Kirill A. Shutemov
2020-04-13 20:48 ` John Hubbard
2020-04-14 21:35 ` Kirill A. Shutemov [this message]
2020-04-15 2:42 ` John Hubbard
2020-04-15 2:43 ` John Hubbard
2020-04-15 20:39 ` Yang Shi
2020-04-13 12:52 ` [PATCHv3, RESEND 6/8] khugepaged: Allow to collapse PTE-mapped compound pages Kirill A. Shutemov
2020-04-15 20:46 ` Yang Shi
2020-04-15 21:44 ` Andrew Morton
2020-04-15 21:52 ` Kirill A. Shutemov
2020-04-15 22:52 ` Andrew Morton
2020-04-15 22:59 ` Kirill A. Shutemov
2020-04-13 12:52 ` [PATCHv3, RESEND 7/8] thp: Change CoW semantics for anon-THP Kirill A. Shutemov
2020-04-15 21:19 ` Yang Shi
2020-04-13 12:52 ` [PATCHv3, RESEND 8/8] khugepaged: Introduce 'max_ptes_shared' tunable Kirill A. Shutemov
2020-04-15 21:25 ` Yang Shi
2020-04-16 15:52 ` Kirill A. Shutemov
2020-04-16 18:25 ` Yang Shi
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