linux-kernel - Re: [PATCH] swiotlb: suppress warning when __GFP

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Date:   Tue, 2 Jan 2018 17:14:17 +0100
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Chris Wilson <chris@...is-wilson.co.uk>, imirkin@...m.mit.edu,
        efault@....de, michel@...nzer.net, konrad.wilk@...cle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] swiotlb: suppress warning when __GFP_NOWARN is set v2

Am 02.01.2018 um 16:39 schrieb Chris Wilson:
> Quoting Christian König (2018-01-02 12:13:58)
>> TTM tries to allocate coherent memory in chunks of 2MB first to improve
>> TLB efficiency and falls back to allocating 4K pages if that fails.
>>
>> Suppress the warning when the 2MB allocations fails since there is a
>> valid fall back path.
>>
>> v2: suppress warnings from swiotlb_tbl_map_single as well
>>
>> Signed-off-by: Christian König <christian.koenig@....com>
>> Reported-by: Mike Galbraith <efault@....de>
>> Bug: https://bugs.freedesktop.org/show_bug.cgi?id=104082
>> CC: stable@...r.kernel.org
>> ---
>> @@ -989,7 +1002,8 @@ swiotlb_map_sg_attrs(struct device *hwdev, struct scatterlist *sgl, int nelems,
>>                  if (swiotlb_force == SWIOTLB_FORCE ||
>>                      !dma_capable(hwdev, dev_addr, sg->length)) {
>>                          phys_addr_t map = map_single(hwdev, sg_phys(sg),
>> -                                                    sg->length, dir, attrs);
>> +                                                    sg->length, dir, attrs,
>> +                                                    true);
> This keeps the warning for dma_map_sg(), so seems quite ineffective.

That is the desired result, dma_map_sg() should still print the warning.

We only want to disable it for swiotlb_alloc_coherent().

Regards,
Christian.

>
>>                          if (map == SWIOTLB_MAP_ERROR) {
>>                                  /* Don't panic here, we expect map_sg users
>>                                     to do proper error handling. */
> And counter to the suggestion here?

We don't use swiotlb_map_sg_attrs() in TTM, so that is irrelevant for my 
use case and I can't test any change regarding it.

Regards,
Christian.

> -Chris