linux-kernel - Re: [PATCH v2] iommu/iova: Try harder to allocate from rcache magazine

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Date:   Thu, 28 Sep 2017 15:41:16 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iommu/iova: Try harder to allocate from rcache
 magazine

On Thu, Sep 28, 2017 at 11:31:23AM +0100, Robin Murphy wrote:
> When devices with different DMA masks are using the same domain, or for
> PCI devices where we usually try a speculative 32-bit allocation first,
> there is a fair possibility that the top PFN of the rcache stack at any
> given time may be unsuitable for the lower limit, prompting a fallback
> to allocating anew from the rbtree. Consequently, we may end up
> artifically increasing pressure on the 32-bit IOVA space as unused IOVAs
> accumulate lower down in the rcache stacks, while callers with 32-bit
> masks also impose unnecessary rbtree overhead.
> 
> In such cases, let's try a bit harder to satisfy the allocation locally
> first - scanning the whole stack should still be relatively inexpensive.
> 
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
> 
> v2: There's no need for a 'proper' stack rotation
> 
>  drivers/iommu/iova.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)

Thanks, applied the series.