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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Date:   Wed, 1 Mar 2023 01:59:47 +0000
From:   Nadav Amit <namit@...are.com>
To:     Peter Xu <peterx@...hat.com>
CC:     Muhammad Usama Anjum <usama.anjum@...labora.com>,
        Mike Rapoport <rppt@...nel.org>,
        Michał Mirosław <emmir@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Paul Gofman <pgofman@...eweavers.com>,
        Danylo Mocherniuk <mdanylo@...gle.com>,
        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>,
        kernel list <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        linux-kselftest <linux-kselftest@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "kernel@...labora.com" <kernel@...labora.com>,
        David Hildenbrand <david@...hat.com>,
        Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCH v10 3/6] fs/proc/task_mmu: Implement IOCTL to get and/or
 the clear info about PTEs



> On Feb 28, 2023, at 11:31 AM, Peter Xu <peterx@...hat.com> wrote:
> 
>> Anyhow, thanks for all the explanations. Eventually, I understand that
>> using bitmaps can be more efficient than a log if the bits are condensed.
> 
> Note that I think what Muhammad (sorry, Muhammad! I think I spelled your
> name wrongly before starting from some email..) proposed is not a bitmap,
> but an array of ranges that can coalesce the result into very condensed
> form.  Pros and cons.
> 
> Again, I can't comment much on that API, but since there're a bunch of
> other developers looking at that and they're also potential future users,
> I'll trust their judgement and just focus more on the other side of things.


Thanks Peter for your patience.

I would just note that I understood that Muhammad did not propose a condensed
bitmap, and that was a hint that handling a condensed bitmap (at least on x86)
can be done rather efficiently. I am not sure about other representations.

Thanks for your explanations again, Peter.