linux-kernel - Re: [PATCH v32 2/6] fs/proc/task_mmu: Implement IOCTL to get and optionally clear info about PTEs

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Message-ID: <ZOAVEFniF/dm+mre@qmqm.qmqm.pl>
Date:   Sat, 19 Aug 2023 03:04:16 +0200
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc:     Peter Xu <peterx@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michał Mirosław <emmir@...gle.com>,
        Andrei Vagin <avagin@...il.com>,
        Danylo Mocherniuk <mdanylo@...gle.com>,
        Paul Gofman <pgofman@...eweavers.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,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v32 2/6] fs/proc/task_mmu: Implement IOCTL to get and
 optionally clear info about PTEs

On Wed, Aug 16, 2023 at 04:30:45PM +0500, Muhammad Usama Anjum wrote:
> The PAGEMAP_SCAN IOCTL on the pagemap file can be used to get or optionally
> clear the info about page table entries.
[...]
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
[...]
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static unsigned long pagemap_thp_category(pmd_t pmd)
> +{
> +	unsigned long categories = PAGE_IS_HUGE;
> +
> +	/*
> +	 * THPs don't support file-backed memory. So PAGE_IS_FILE
> +	 * is not checked here.
> +	 */

It seems that we can have THP for files: ref. recent LKML thread [1].

[1] https://lkml.org/lkml/2023/8/16/1212

> +	if (pmd_present(pmd)) {
> +		categories |= PAGE_IS_PRESENT;
> +		if (!pmd_uffd_wp(pmd))
> +			categories |= PAGE_IS_WRITTEN;
> +		if (is_zero_pfn(pmd_pfn(pmd)))
> +			categories |= PAGE_IS_PFNZERO;
> +	} else if (is_swap_pmd(pmd)) {
> +		categories |= PAGE_IS_SWAPPED;
> +		if (!pmd_swp_uffd_wp(pmd))
> +			categories |= PAGE_IS_WRITTEN;
> +	}
> +
> +	return categories;
> +}

Best Regards
Michał Mirosław