linux-kernel - Re: [PATCH v10 3/6] fs/proc/task_mmu: Implement IOCTL to get and/or the clear info about PTEs

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Message-ID: <CABb0KFEgsk+YidSXBYQ9mM8nVV6PuEOQf=bbNn7hsoG1hUeLZg@mail.gmail.com>
Date:   Fri, 17 Feb 2023 16:18:47 +0100
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>,
        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>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.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 v10 3/6] fs/proc/task_mmu: Implement IOCTL to get and/or
 the clear info about PTEs

On Thu, 2 Feb 2023 at 12:30, Muhammad Usama Anjum
<usama.anjum@...labora.com> wrote:
[...]
> - The masks are specified in required_mask, anyof_mask, excluded_ mask
>   and return_mask.
[...]

May I suggest a slightly modified interface for the flags?

As I understand, the return_mask is what is applied to page flags to
aggregate the list.
This is a separate thing, and I think it doesn't need changes except
maybe an improvement
in the documentation and visual distinction.

For the page-selection mechanism, currently required_mask and
excluded_mask have conflicting
responsibilities. I suggest to rework that to:
1. negated_flags: page flags which are to be negated before applying
the page selection using following masks;
2. required_flags: flags which all have to be set in the
(negation-applied) page flags;
3. anyof_flags: flags of which at least one has to be set in the
(negation-applied) page flags;

IOW, the resulting algorithm would be:

tested_flags = page_flags ^ negated_flags;
if (~tested_flags & required_flags)
  skip page;
if (!(tested_flags & anyof_flags))
  skip_page;

aggregate_on(page_flags & return_flags);

Best Regards
Michał Mirosław