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

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Message-ID: <20210503182434.GA17174@lst.de>
Date:   Mon, 3 May 2021 20:24:35 +0200
From:   Christoph Hellwig <hch@....de>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     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,
        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 Mon, May 03, 2021 at 11:17:31AM -0700, John Hubbard 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.

Agreed.