From: Dave Hansen <dave.hansen@intel.com>
To: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@kernel.org>,
linux-next@vger.kernel.org, akpm@linux-foundation.org,
jack@suse.cz, kirill@shutemov.name, "Edgecombe,
Rick P" <rick.p.edgecombe@intel.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
borntraeger@de.ibm.com, david@redhat.com, aarcange@redhat.com,
linux-mm@kvack.org, frankja@linux.ibm.com, sfr@canb.auug.org.au,
jhubbard@nvidia.com, linux-kernel@vger.kernel.org,
linux-s390@vger.kernel.org, Will Deacon <will@kernel.org>,
"Williams, Dan J" <dan.j.williams@intel.com>
Subject: Re: [PATCH v4 2/2] mm/gup/writeback: add callbacks for inaccessible pages
Date: Tue, 21 Apr 2020 14:31:28 -0700 [thread overview]
Message-ID: <cbaddd28-c5d3-61a2-84d8-c883fb3d6290@intel.com> (raw)
In-Reply-To: <396a4ece-ec66-d023-2c7e-f09f84b358bc@intel.com>
On 4/16/20 12:02 PM, Dave Hansen wrote:
> On 4/16/20 9:34 AM, Claudio Imbrenda wrote:
>>> Ahh, so this is *just* intended to precede I/O done on the page, when
>>> a non-host entity is touching the memory?
>> yep
> OK, so we've got to do an action that precedes *all* I/O to a page.
> That's not too bad.
>
> I still don't understand how this could work generally, though There
> are lots of places where I/O is done to a page without either going
> through __test_set_page_writeback() or gup() with FOLL_PIN set.
>
> sendfile() is probably the best example of this:
>
> fd = open("/normal/ext4/file", O_RDONLY);
> sendfile(socket_fd, fd, &off, count);
>
> There's no gup in sight since the file doesn't have an address and it's
> not being written to so there's no writeback.
>
> How does sendfile work?
Did you manage to see if sendfile works (or any other operation that
DMAs file-backed data without being preceded by a gup)?
I suspect it's actually not that hard to fix. As long as you have a
dma_ops for the devices in question either via dev->dma_ops or you add
an s390 get_arch_vm_ops(), you can fix *all* the DMA sites, sendfile()
included.
BTW, device drivers do need to know how to use the DMA mapping API. If
s390 has drivers that need to be updated, I think that's vastly
preferable to incomplete hooks in core mm code.
next prev parent reply other threads:[~2020-04-21 21:31 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-06 13:25 [PATCH v4 0/2] add callbacks for inaccessible pages Claudio Imbrenda
2020-03-06 13:25 ` [PATCH v4 1/2] mm/gup: fixup for 9947ea2c1e608e32 "mm/gup: track FOLL_PIN pages" Claudio Imbrenda
2020-03-06 13:25 ` [PATCH v4 2/2] mm/gup/writeback: add callbacks for inaccessible pages Claudio Imbrenda
2020-04-13 20:22 ` Dave Hansen
2020-04-14 16:03 ` Claudio Imbrenda
2020-04-14 18:50 ` Dave Hansen
2020-04-15 9:26 ` Claudio Imbrenda
2020-04-15 11:39 ` Janosch Frank
2020-04-15 21:52 ` Dave Hansen
2020-04-15 22:17 ` Peter Zijlstra
2020-04-15 23:34 ` Dave Hansen
2020-04-16 12:15 ` Claudio Imbrenda
2020-04-16 14:20 ` Dave Hansen
2020-04-16 14:59 ` Claudio Imbrenda
2020-04-16 15:36 ` Dave Hansen
2020-04-16 16:34 ` Claudio Imbrenda
2020-04-16 19:02 ` Dave Hansen
2020-04-21 21:31 ` Dave Hansen [this message]
2020-04-28 19:43 ` Dave Hansen
2020-04-28 20:02 ` Christian Borntraeger
2020-04-28 23:39 ` Claudio Imbrenda
2020-04-29 0:42 ` Dave Hansen
2020-04-16 11:51 ` Claudio Imbrenda
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