Re: [PATCH] virtio_balloon: high order allocation

From: Soichiro Ueda <the.latticeheart@gmail.com>
To: David Hildenbrand <david@redhat.com>,
	mst@redhat.com, jasowang@redhat.com, akpm@linux-foundation.org
Cc: virtualization@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	kalutes@google.com, mhiramat@kernel.org, cwd@google.com
Subject: Re: [PATCH] virtio_balloon: high order allocation
Date: Thu, 29 Dec 2022 14:31:48 +0900	[thread overview]
Message-ID: <444735fd-7076-7bd3-dc5e-7135a7f3a95c@gmail.com> (raw)
In-Reply-To: <c8ea7076-f107-c340-6b34-6b22a9369da5@redhat.com>

Hi David.

> How does this affect page migration / balloon compaction etc?

I guess this patch doesn't affect balloon compaction. When allocating 
pages using alloc_pages(), it skips compaction by masking out 
__GFP_RECLAIM if the order is larger than 0.

As for page migration, in the current implementation it migrate a 
0-order page to another 0-order page. With this patch, it may migrate a 
high-order page to another same-order page.

But I noticed that the migrated high-order page is handled as 0-order 
page in virtballoon_migratepage().

 >     balloon_page_insert(vb_dev_info, newpage);

We should put the newpage into a page list of the corresponding order, 
like this.

     balloon_page_enqueue(vb_dev_info, newpage, order);

I'll fix it in the v2 patch.

Thank you,