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Message-ID: <CABb0KFF+sKSv7jdxBbXpt5A2WO83tKb9viq-kKurXN_e1VcFhQ@mail.gmail.com>
Date: Fri, 7 Apr 2023 09:23:55 +0200
From: Michał Mirosław <emmir@...gle.com>
To: Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc: Peter Xu <peterx@...hat.com>, David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Andrei Vagin <avagin@...il.com>,
Danylo Mocherniuk <mdanylo@...gle.com>,
Paul Gofman <pgofman@...eweavers.com>,
Cyrill Gorcunov <gorcunov@...il.com>,
Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
Shuah Khan <shuah@...nel.org>,
Christian Brauner <brauner@...nel.org>,
Yang Shi <shy828301@...il.com>,
Vlastimil Babka <vbabka@...e.cz>,
"Liam R . Howlett" <Liam.Howlett@...cle.com>,
Yun Zhou <yun.zhou@...driver.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Alex Sierra <alex.sierra@....com>,
Matthew Wilcox <willy@...radead.org>,
Pasha Tatashin <pasha.tatashin@...een.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
"Gustavo A . R . Silva" <gustavoars@...nel.org>,
Dan Williams <dan.j.williams@...el.com>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
Greg KH <gregkh@...uxfoundation.org>, kernel@...labora.com
Subject: Re: [PATCH v12 2/5] fs/proc/task_mmu: Implement IOCTL to get and
optionally clear info about PTEs
On Thu, 6 Apr 2023 at 23:12, Muhammad Usama Anjum
<usama.anjum@...labora.com> wrote:
> On 4/7/23 1:12 AM, Michał Mirosław wrote:
> > On Thu, 6 Apr 2023 at 09:40, Muhammad Usama Anjum
> > <usama.anjum@...labora.com> wrote:
> > [...]
> >> --- a/fs/proc/task_mmu.c
> >> +++ b/fs/proc/task_mmu.c
> > [...]
> >> +static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
> >> + unsigned long end, struct mm_walk *walk)
> >> +{
[...]
> >> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> >> + ptl = pmd_trans_huge_lock(pmd, vma);
> >> + if (ptl) {
> > [...]
> >> + return ret;
> >> + }
> >> +process_smaller_pages:
> >> + if (pmd_trans_unstable(pmd))
> >> + return 0;
> >
> > Why pmd_trans_unstable() is needed here and not only after split_huge_pmd()?
> I'm not entirely sure. But the idea is if THP is unstable, we should
> return. As it doesn't seem like after splitting THP can be unstable, we
> should not check it. Do you agree with the following?
The description of pmd_trans_unstable() [1] seems to indicate that it
is needed only after split_huge_pmd().
[1] https://elixir.bootlin.com/linux/v6.3-rc5/source/include/linux/pgtable.h#L1394
Best Regards
Michał Mirosław
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