linux-kernel - Re: [PATCH] virtio_balloon: high order allocation

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Message-ID: <444735fd-7076-7bd3-dc5e-7135a7f3a95c@gmail.com>
Date:   Thu, 29 Dec 2022 14:31:48 +0900
From:   Soichiro Ueda <the.latticeheart@...il.com>
To:     David Hildenbrand <david@...hat.com>, mst@...hat.com,
        jasowang@...hat.com, akpm@...ux-foundation.org
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kalutes@...gle.com, mhiramat@...nel.org, cwd@...gle.com
Subject: Re: [PATCH] virtio_balloon: high order allocation

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,