Re: [RFC][PATCH 1/4] mm, page_owner: add folio allocate post callback for struct page_owner to make the owner clearer

From: Matthew Wilcox <willy@infradead.org>
To: Jeff Xie <jeff.xie@linux.dev>
Cc: akpm@linux-foundation.org, iamjoonsoo.kim@lge.com,
	vbabka@suse.cz, cl@linux.com, penberg@kernel.org,
	rientjes@google.com, roman.gushchin@linux.dev,
	42.hyeyoo@gmail.com, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	chensong_2000@189.cn, xiehuan09@gmail.com
Subject: Re: [RFC][PATCH 1/4] mm, page_owner: add folio allocate post callback for struct page_owner to make the owner clearer
Date: Thu, 9 Nov 2023 13:59:45 +0000	[thread overview]
Message-ID: <ZUzl0U++a5fRpCQm@casper.infradead.org> (raw)
In-Reply-To: <20231109032521.392217-2-jeff.xie@linux.dev>

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