linux-kernel - Re: [RFC PATCH 1/2] xen/unpopulated-alloc: Introduce helpers for DMA allocations

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Message-ID: <YqrunrtBjWPgdlDi@Air-de-Roger>
Date:   Thu, 16 Jun 2022 10:49:34 +0200
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Stefano Stabellini <sstabellini@...nel.org>
Cc:     Oleksandr <olekstysh@...il.com>, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, Julien Grall <julien@....org>
Subject: Re: [RFC PATCH 1/2] xen/unpopulated-alloc: Introduce helpers for DMA
 allocations

On Tue, Jun 14, 2022 at 05:45:53PM -0700, Stefano Stabellini wrote:
> Basically, if we allocate (and free) page-by-page it leads to more
> efficient resource utilization but it is slower. If we allocate larger
> contiguous chunks it is faster but it leads to less efficient resource
> utilization.
> 
> Given that on both x86 and ARM the unpopulated memory resource is
> arbitrarily large, I don't think we need to worry about resource
> utilization. It is not backed by real memory. The only limitation is the
> address space size which is very large.

Well, unpopulated memory will consume memory to populate the related
metadata (ie: struct page and realted tracking information) for the
unpopulated region, so it's not completely free.

Thanks, Roger.