MIME-Version: 1.0
References: <20230202112915.867409-1-usama.anjum@collabora.com> <20230202112915.867409-4-usama.anjum@collabora.com>
In-Reply-To: <20230202112915.867409-4-usama.anjum@collabora.com>
From:   =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <emmir@google.com>
Date:   Fri, 17 Feb 2023 16:18:47 +0100
Message-ID: <CABb0KFEgsk+YidSXBYQ9mM8nVV6PuEOQf=bbNn7hsoG1hUeLZg@mail.gmail.com>
Subject: Re: [PATCH v10 3/6] fs/proc/task_mmu: Implement IOCTL to get and/or
 the clear info about PTEs
To:     Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc:     Peter Xu <peterx@redhat.com>, David Hildenbrand <david@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrei Vagin <avagin@gmail.com>,
        Danylo Mocherniuk <mdanylo@google.com>,
        Paul Gofman <pgofman@codeweavers.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Shuah Khan <shuah@kernel.org>,
        Christian Brauner <brauner@kernel.org>,
        Yang Shi <shy828301@gmail.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Liam R . Howlett" <Liam.Howlett@oracle.com>,
        Yun Zhou <yun.zhou@windriver.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Alex Sierra <alex.sierra@amd.com>,
        Matthew Wilcox <willy@infradead.org>,
        Pasha Tatashin <pasha.tatashin@soleen.com>,
        Mike Rapoport <rppt@kernel.org>, Nadav Amit <namit@vmware.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        "Gustavo A . R . Silva" <gustavoars@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
        Greg KH <gregkh@linuxfoundation.org>, kernel@collabora.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Thu, 2 Feb 2023 at 12:30, Muhammad Usama Anjum
<usama.anjum@collabora.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 =3D 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
Micha=C5=82 Miros=C5=82aw