linux-kernel - Re: [PATCH 01/16] PCI/P2PDMA: Pass gfp_mask flags to upstream_bridge_distance

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Date:   Mon, 3 May 2021 11:23:43 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        <linux-kernel@...r.kernel.org>, <linux-nvme@...ts.infradead.org>,
        <linux-block@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-mm@...ck.org>, <iommu@...ts.linux-foundation.org>
CC:     Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 01/16] PCI/P2PDMA: Pass gfp_mask flags to
 upstream_bridge_distance_warn()

On 5/3/21 11:20 AM, Logan Gunthorpe wrote:
...
>> That's the thing: memory failure should be exceedingly rare for this.
>> Therefore, just fail out entirely (which I don't expect we'll likely
>> ever see), instead of doing all this weird stuff to try to continue
>> on if you cannot allocate a single page. If you are in that case, the
>> system is not in a state that is going to run your dma p2p setup well
>> anyway.
>>
>> I think it's *less* complexity to allocate up front, fail early if
>> allocation fails, and then not have to deal with these really odd
>> quirks at the lower levels.
>>
> 
> I don't see how it's all that weird. We're skipping a warning if we
> can't allocate memory to calculate part of the message. It's really not
> necessary. If the memory really can't be allocated then something else
> will fail, but we really don't need to fail here because we couldn't
> print a verbose warning message.
> 

Well, I really dislike the result we have in this particular patch, but
I won't stand in the way of progress if that's how you really are going
to do it.

thanks,
-- 
John Hubbard
NVIDIA