linux-kernel - Re: [v3] fs/proc/task_mmu: Implement IOCTL for efficient page table scanning

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Date:   Tue, 25 Jul 2023 20:05:32 +0200
From:   Michał Mirosław <emmir@...gle.com>
To:     Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc:     Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Andrei Vagin <avagin@...il.com>,
        Danylo Mocherniuk <mdanylo@...gle.com>,
        Alex Sierra <alex.sierra@....com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Christian Brauner <brauner@...nel.org>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Paul Gofman <pgofman@...eweavers.com>,
        Peter Xu <peterx@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Yang Shi <shy828301@...il.com>,
        Yun Zhou <yun.zhou@...driver.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [v3] fs/proc/task_mmu: Implement IOCTL for efficient page table scanning

On Tue, 25 Jul 2023 at 11:11, Muhammad Usama Anjum
<usama.anjum@...labora.com> wrote:
>
> ----
> Michal please post your thoughts before I post this as v26.
> ----
[...]

Looks ok - minor things below.

1. I'd change the _WPASYNC things to something better, if this can
also work with "normal" UFFD WP.

2. For the address tagging part I'd prefer someone who knows how this
is used take a look. We're ignoring the tag (but clear it on return in
->start) - so it doesn't matter for the ioctl() itself.

3. BTW, One of the uses is the GetWriteWatch and I wonder how it
behaves on HugeTLB (MEM_LARGE_PAGES allocation)? Shouldn't it return a
list of huge pages and write *lpdwGranularity = HPAGE_SIZE?

4. The docs and commit messages need some rewording due to the changes
in the API.

Other than that:

Reviewed-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>