linux-kernel - Re: [PATCH v9 3/5] mm: function to offer a page block on the free list

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Date:   Thu, 13 Apr 2017 13:02:17 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Wei Wang <wei.w.wang@...el.com>
Cc:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, mst@...hat.com,
        david@...hat.com, dave.hansen@...el.com, cornelia.huck@...ibm.com,
        mgorman@...hsingularity.net, aarcange@...hat.com,
        amit.shah@...hat.com, pbonzini@...hat.com,
        liliang.opensource@...il.com
Subject: Re: [PATCH v9 3/5] mm: function to offer a page block on the free
 list

On Thu, 13 Apr 2017 17:35:06 +0800 Wei Wang <wei.w.wang@...el.com> wrote:

> Add a function to find a page block on the free list specified by the
> caller. Pages from the page block may be used immediately after the
> function returns. The caller is responsible for detecting or preventing
> the use of such pages.
> 
> ...
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4498,6 +4498,93 @@ void show_free_areas(unsigned int filter)
>  	show_swap_cache_info();
>  }
>  
> +/**
> + * Heuristically get a page block in the system that is unused.
> + * It is possible that pages from the page block are used immediately after
> + * inquire_unused_page_block() returns. It is the caller's responsibility
> + * to either detect or prevent the use of such pages.
> + *
> + * The free list to check: zone->free_area[order].free_list[migratetype].
> + *
> + * If the caller supplied page block (i.e. **page) is on the free list, offer
> + * the next page block on the list to the caller. Otherwise, offer the first
> + * page block on the list.
> + *
> + * Return 0 when a page block is found on the caller specified free list.
> + */
> +int inquire_unused_page_block(struct zone *zone, unsigned int order,
> +			      unsigned int migratetype, struct page **page)
> +{

Perhaps we can wrap this in the appropriate ifdef so the kernels which
won't be using virtio-balloon don't carry the added overhead.