linux-kernel - Re: [RFC][PATCH 1/4] mm, page_owner: add folio allocate post callback for struct page

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Message-ID: <ZUzl0U++a5fRpCQm@casper.infradead.org>
Date:   Thu, 9 Nov 2023 13:59:45 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Jeff Xie <jeff.xie@...ux.dev>
Cc:     akpm@...ux-foundation.org, iamjoonsoo.kim@....com, vbabka@...e.cz,
        cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        roman.gushchin@...ux.dev, 42.hyeyoo@...il.com, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        chensong_2000@....cn, xiehuan09@...il.com
Subject: Re: [RFC][PATCH 1/4] mm, page_owner: add folio allocate post
 callback for struct page_owner to make the owner clearer

On Thu, Nov 09, 2023 at 11:25:18AM +0800, Jeff Xie wrote:
> adding a callback function in the struct page_owner to let the slab layer or the
> anon/file handler layer or any other memory-allocated layers to implement what
> they would like to tell.

There's no need to add a callback.  We can tell what a folio is.

> +	if (page_owner->folio_alloc_post_page_owner) {
> +		rcu_read_lock();
> +		tsk = find_task_by_pid_ns(page_owner->pid, &init_pid_ns);
> +		rcu_read_unlock();
> +		ret += page_owner->folio_alloc_post_page_owner(page_folio(page), tsk, page_owner->data,
> +				kbuf + ret, count - ret);
> +	} else
> +		ret += scnprintf(kbuf + ret, count - ret, "OTHER_PAGE\n");

	if (folio_test_slab(folio))
		ret += slab_page_owner_info(folio, kbuf + ret, count - ret);
	else if (folio_test_anon(folio))
		ret += anon_page_owner_info(folio, kbuf + ret, count - ret);
	else if (folio_test_movable(folio))
		ret += null_page_owner_info(folio, kbuf + ret, count - ret);
	else if (folio->mapping)
		ret += file_page_owner_info(folio, kbuf + ret, count - ret);
	else
		ret += null_page_owner_info(folio, kbuf + ret, count - ret);

In this scenario, I have the anon handling ksm pages, but if that's not
desirable, we can add

	else if (folio_test_ksm(folio))
		ret += ksm_page_owner_info(folio, kbuf + ret, count - ret);

right before the folio_test_anon() clause