From: Benjamin Herrenschmidt <benh-XVmvHMARGAS8U2dJNN8I7kB+6BGkLq7r@public.gmane.org>
To: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
Cc: Greg Kroah-Hartman
<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>,
Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org,
linuxppc-dev-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org
Subject: Re: [PATCH 3/5] dma-direct: refine dma_direct_alloc zone selection
Date: Fri, 28 Sep 2018 10:06:48 +1000 [thread overview]
Message-ID: <514bd29960cb1573ead2f3956f18e1cbaa5f32f7.camel@kernel.crashing.org> (raw)
In-Reply-To: <20180927134922.GA8281-jcswGhMUV9g@public.gmane.org>
On Thu, 2018-09-27 at 15:49 +0200, Christoph Hellwig wrote:
> On Thu, Sep 27, 2018 at 11:45:15AM +1000, Benjamin Herrenschmidt wrote:
> > I'm not sure this is entirely right.
> >
> > Let's say the mask is 30 bits. You will return GFP_DMA32, which will
> > fail if you allocate something above 1G (which is legit for
> > ZONE_DMA32).
>
> And then we will try GFP_DMA further down in the function:
>
> if (IS_ENABLED(CONFIG_ZONE_DMA) &&
> dev->coherent_dma_mask < DMA_BIT_MASK(32) &&
> !(gfp & GFP_DMA)) {
> gfp = (gfp & ~GFP_DMA32) | GFP_DMA;
> goto again;
> }
>
> This is and old optimization from x86, because chances are high that
> GFP_DMA32 will give you suitable memory for the infamous 31-bit
> dma mask devices (at least at boot time) and thus we don't have
> to deplete the tiny ZONE_DMA pool.
I see, it's rather confusing :-) Wouldn't it be better to check against
top of 32-bit memory instead here too ?
Cheers,
Ben.
next prev parent reply other threads:[~2018-09-28 0:06 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-20 18:52 dma mask related fixups (including full bus_dma_mask support) Christoph Hellwig
2018-09-20 18:52 ` [PATCH 1/5] dma-mapping: make the get_required_mask method available unconditionally Christoph Hellwig
[not found] ` <20180920185247.20037-2-hch-jcswGhMUV9g@public.gmane.org>
2018-09-27 1:28 ` Benjamin Herrenschmidt
2018-09-20 18:52 ` [PATCH 2/5] dma-direct: add an explicit dma_direct_get_required_mask Christoph Hellwig
[not found] ` <20180920185247.20037-3-hch-jcswGhMUV9g@public.gmane.org>
2018-09-27 1:31 ` Benjamin Herrenschmidt
2018-09-27 14:12 ` Robin Murphy
2018-09-27 15:28 ` Christoph Hellwig
[not found] ` <20180927152818.GC10566-jcswGhMUV9g@public.gmane.org>
2018-09-27 15:35 ` Robin Murphy
2018-09-20 18:52 ` [PATCH 3/5] dma-direct: refine dma_direct_alloc zone selection Christoph Hellwig
[not found] ` <20180920185247.20037-4-hch-jcswGhMUV9g@public.gmane.org>
2018-09-27 1:45 ` Benjamin Herrenschmidt
[not found] ` <1811156d5a1df1166c7ab7522525619b951f047d.camel-XVmvHMARGAS8U2dJNN8I7kB+6BGkLq7r@public.gmane.org>
2018-09-27 13:49 ` Christoph Hellwig
[not found] ` <20180927134922.GA8281-jcswGhMUV9g@public.gmane.org>
2018-09-28 0:06 ` Benjamin Herrenschmidt [this message]
2018-09-28 15:46 ` Christoph Hellwig
2018-09-27 14:30 ` Robin Murphy
2018-09-27 15:30 ` Christoph Hellwig
[not found] ` <20180927153028.GD10566-jcswGhMUV9g@public.gmane.org>
2018-09-27 15:38 ` Robin Murphy
[not found] ` <2b98d7b2-bf74-ccc9-881a-a91e2c9949c3-5wv7dgnIgG8@public.gmane.org>
2018-09-27 15:41 ` Christoph Hellwig
2018-09-20 18:52 ` [PATCH 4/5] dma-direct: implement complete bus_dma_mask handling Christoph Hellwig
[not found] ` <20180920185247.20037-5-hch-jcswGhMUV9g@public.gmane.org>
2018-09-27 14:58 ` Robin Murphy
2018-09-27 15:32 ` Christoph Hellwig
2018-09-27 16:14 ` Robin Murphy
[not found] ` <967e98b1-99ab-8f95-4c89-6156ce489b93-5wv7dgnIgG8@public.gmane.org>
2018-09-27 16:27 ` Christoph Hellwig
[not found] ` <20180927162737.GA11974-jcswGhMUV9g@public.gmane.org>
2018-09-27 16:41 ` Robin Murphy
2018-09-20 18:52 ` [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory size Christoph Hellwig
[not found] ` <20180920185247.20037-6-hch-jcswGhMUV9g@public.gmane.org>
2018-09-27 1:50 ` Benjamin Herrenschmidt
2018-09-27 13:49 ` Christoph Hellwig
2018-09-27 15:07 ` Robin Murphy
-- strict thread matches above, loose matches on Subject: below --
2018-09-27 22:35 dma mask related fixups (including full bus_dma_mask support) v2 Christoph Hellwig
2018-09-27 22:35 ` [PATCH 3/5] dma-direct: refine dma_direct_alloc zone selection Christoph Hellwig
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