From: Oliver Neukum <oneukum@suse.com>
To: Christoph Hellwig <hch@infradead.org>,
Alan Stern <stern@rowland.harvard.edu>
Cc: Jaewon Kim <jaewon31.kim@gmail.com>,
linux-mm@kvack.org, gregkh@linuxfoundation.org,
Jaewon Kim <jaewon31.kim@samsung.com>,
m.szyprowski@samsung.com, ytk.lee@samsung.com,
linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org
Subject: Re: [RFC PATCH] usb: host: xhci: allow __GFP_FS in dma allocation
Date: Tue, 21 May 2019 10:54:37 +0200 [thread overview]
Message-ID: <1558428877.12672.8.camel@suse.com> (raw)
In-Reply-To: <20190520142331.GA12108@infradead.org>
On Mo, 2019-05-20 at 07:23 -0700, Christoph Hellwig wrote:
> On Mon, May 20, 2019 at 10:16:57AM -0400, Alan Stern wrote:
> > What if the allocation requires the kernel to swap some old pages out
> > to the backing store, but the backing store is on the device that the
> > driver is managing? The swap can't take place until the current I/O
> > operation is complete (assuming the driver can handle only one I/O
> > operation at a time), and the current operation can't complete until
> > the old pages are swapped out. Result: deadlock.
> >
> > Isn't that the whole reason for using GFP_NOIO in the first place?
>
> It is, or rather was. As it has been incredibly painful to wire
> up the gfp_t argument through some callstacks, most notably the
> vmalloc allocator which is used by a lot of the DMA allocators on
> non-coherent platforms, we now have the memalloc_noio_save and
> memalloc_nofs_save functions that mark a thread as not beeing to
> go into I/O / FS reclaim. So even if you use GFP_KERNEL you will
> not dip into reclaim with those flags set on the thread.
OK, but this leaves a question open. Will the GFP_NOIO actually
hurt, if it is used after memalloc_noio_save()?
Regards
Oliver
next prev parent reply other threads:[~2019-05-21 9:07 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-17 16:02 [RFC PATCH] usb: host: xhci: allow __GFP_FS in dma allocation Jaewon Kim
2019-05-17 16:34 ` Matthew Wilcox
2019-05-18 1:53 ` Jaewon Kim
2019-05-20 5:56 ` Christoph Hellwig
2019-05-20 9:09 ` Oliver Neukum
2019-05-20 10:12 ` Christoph Hellwig
2019-05-20 14:16 ` Alan Stern
2019-05-20 14:23 ` Christoph Hellwig
2019-05-21 8:54 ` Oliver Neukum [this message]
2019-05-21 13:27 ` Christoph Hellwig
2019-05-21 13:11 ` Oliver Neukum
2019-05-21 14:00 ` Alan Stern
2019-05-22 6:31 ` Oliver Neukum
2019-05-22 14:56 ` Alan Stern
2019-05-22 20:47 ` Oliver Neukum
2019-05-23 14:01 ` Alan Stern
2019-05-28 12:34 ` Oliver Neukum
2019-05-28 14:25 ` Alan Stern
2019-05-23 12:32 ` Oliver Neukum
2019-05-23 16:35 ` Christoph Hellwig
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