linux-kernel - Re: [PATCH v12 2/5] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

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Message-ID: <CABb0KFFTb3LCbyPWLSodtntw=tizYki-pc4nSHBmQOFhKoNYfA@mail.gmail.com>
Date:   Thu, 6 Apr 2023 22:12:03 +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 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)
> +{
> +       struct pagemap_scan_private *p = walk->private;
> +       bool is_written, is_file, is_present, is_swap;
> +       struct vm_area_struct *vma = walk->vma;
> +       unsigned long addr = end;
> +       spinlock_t *ptl;
> +       int ret = 0;
> +       pte_t *pte;
> +
> +#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()?

Best regards
Michał Mirosław