linux-kernel - Re: [PATCH] iommu/iova: Improve 32-bit free space estimate

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Message-ID: <YiHey3lGHAMUp+oC@8bytes.org>
Date:   Fri, 4 Mar 2022 10:41:31 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Miles Chen <miles.chen@...iatek.com>
Cc:     robin.murphy@....com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, will@...nel.org,
        wsd_upstream@...iatek.com, yf.wang@...iatek.com,
        stable@...r.kernel.org
Subject: Re: [PATCH] iommu/iova: Improve 32-bit free space estimate

On Fri, Mar 04, 2022 at 07:36:46AM +0800, Miles Chen wrote:
> Hi Robin,
> 
> > For various reasons based on the allocator behaviour and typical
> > use-cases at the time, when the max32_alloc_size optimisation was
> > introduced it seemed reasonable to couple the reset of the tracked
> > size to the update of cached32_node upon freeing a relevant IOVA.
> > However, since subsequent optimisations focused on helping genuine
> > 32-bit devices make best use of even more limited address spaces, it
> > is now a lot more likely for cached32_node to be anywhere in a "full"
> > 32-bit address space, and as such more likely for space to become
> > available from IOVAs below that node being freed.
> > 
> > At this point, the short-cut in __cached_rbnode_delete_update() really
> > doesn't hold up any more, and we need to fix the logic to reliably
> > provide the expected behaviour. We still want cached32_node to only move
> > upwards, but we should reset the allocation size if *any* 32-bit space
> > has become available.
> > 
> > Reported-by: Yunfei Wang <yf.wang@...iatek.com>
> > Signed-off-by: Robin Murphy <robin.murphy@....com>
> 
> Would you mind adding:
> 
> Cc: <stable@...r.kernel.org>

Applied without stable tag for now. If needed, please consider
re-sending it for stable when this patch is merged upstream.

Regards,

	Joerg