From: John Hubbard <jhubbard@nvidia.com>
To: Jan Kara <jack@suse.cz>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Alex Williamson" <alex.williamson@redhat.com>,
"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
"Björn Töpel" <bjorn.topel@intel.com>,
"Christoph Hellwig" <hch@infradead.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Daniel Vetter" <daniel@ffwll.ch>,
"Dave Chinner" <david@fromorbit.com>,
"David Airlie" <airlied@linux.ie>,
"David S . Miller" <davem@davemloft.net>,
"Ira Weiny" <ira.weiny@intel.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>, "Jens Axboe" <axboe@kernel.dk>,
"Jonathan Corbet" <corbet@lwn.net>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Magnus Karlsson" <magnus.karlsson@intel.com>,
"Mauro Carvalho Chehab" <mchehab@kernel.org>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Michal Hocko" <mhocko@suse.com>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Paul Mackerras" <paulus@samba.org>,
"Shuah Khan" <shuah@kernel.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
bpf@vger.kernel.org, dri-devel@lists.freedesktop.org,
kvm@vger.kernel.org, linux-block@vger.kernel.org,
linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org,
linux-rdma@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
netdev@vger.kernel.org, linux-mm@kvack.org,
LKML <linux-kernel@vger.kernel.org>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v9 23/25] mm/gup: track FOLL_PIN pages
Date: Wed, 11 Dec 2019 21:53:45 -0800 [thread overview]
Message-ID: <f961d0b6-c660-85b9-ad01-53bce74e39e9@nvidia.com> (raw)
In-Reply-To: <20191211112807.GN1551@quack2.suse.cz>
On 12/11/19 3:28 AM, Jan Kara wrote:
...
>
> The patch looks mostly good to me now. Just a few smaller comments below.
>
>> Suggested-by: Jan Kara <jack@suse.cz>
>> Suggested-by: Jérôme Glisse <jglisse@redhat.com>
>> Reviewed-by: Jan Kara <jack@suse.cz>
>> Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
>> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
>
> I think you inherited here the Reviewed-by tags from the "add flags" patch
> you've merged into this one but that's not really fair since this patch
> does much more... In particular I didn't give my Reviewed-by tag for this
> patch yet.
OK, I've removed those reviewed-by's. (I felt bad about dropping them, after
people had devoted time to reviewing, but I do see that it's wrong to imply
that they've reviewed this much much larger thing.)
...
>
> I somewhat wonder about the asymmetry of try_grab_compound_head() vs
> try_grab_page() in the treatment of 'flags'. How costly would it be to make
> them symmetric (i.e., either set FOLL_GET for try_grab_compound_head()
> callers or make sure one of FOLL_GET, FOLL_PIN is set for try_grab_page())?
>
> Because this difference looks like a subtle catch in the long run...
Done. It is only a modest code-level change, at least the way I've done it, which is
setting FOLL_GET for try_grab_compound_head(). In order to do that, I set
it at the top of the internal gup fast calling stacks, which is actually a good
design anyway: gup fast is logically doing FOLL_GET in all cases. So setting
the flag internally is accurate and consistent with the overall design.
> ...
>
>> @@ -1522,8 +1536,8 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
>> skip_mlock:
>> page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
>> VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
>> - if (flags & FOLL_GET)
>> - get_page(page);
>> + if (!try_grab_page(page, flags))
>> + page = ERR_PTR(-EFAULT);
>
> I think you need to also move the try_grab_page() earlier in the function.
> At this point the page may be marked as mlocked and you'd need to undo that
> in case try_grab_page() fails.
OK, I've moved it up, adding a "subpage" variable in order to make that work.
>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index ac65bb5e38ac..0aab6fe0072f 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -4356,7 +4356,13 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
>> same_page:
>> if (pages) {
>> pages[i] = mem_map_offset(page, pfn_offset);
>> - get_page(pages[i]);
>> + if (!try_grab_page(pages[i], flags)) {
>> + spin_unlock(ptl);
>> + remainder = 0;
>> + err = -ENOMEM;
>> + WARN_ON_ONCE(1);
>> + break;
>> + }
>> }
>
> This function does a refcount overflow check early so that it doesn't have
> to do try_get_page() here. So that check can be now removed when you do
> try_grab_page() here anyway since that early check seems to be just a tiny
> optimization AFAICT.
>
> Honza
>
Yes. I've removed it, good spot.
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2019-12-12 5:56 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-11 2:52 [PATCH v9 00/25] mm/gup: track dma-pinned pages: FOLL_PIN John Hubbard
2019-12-11 2:52 ` [PATCH v9 01/25] mm/gup: factor out duplicate code from four routines John Hubbard
2019-12-11 2:52 ` [PATCH v9 02/25] mm/gup: move try_get_compound_head() to top, fix minor issues John Hubbard
2019-12-11 2:52 ` [PATCH v9 03/25] mm: Cleanup __put_devmap_managed_page() vs ->page_free() John Hubbard
2019-12-11 2:52 ` [PATCH v9 04/25] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages John Hubbard
2019-12-11 2:52 ` [PATCH v9 05/25] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-12-11 2:52 ` [PATCH v9 06/25] mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM John Hubbard
2019-12-11 2:53 ` [PATCH v9 07/25] vfio: fix FOLL_LONGTERM use, simplify get_user_pages_remote() call John Hubbard
2019-12-11 2:53 ` [PATCH v9 08/25] mm/gup: allow FOLL_FORCE for get_user_pages_fast() John Hubbard
2019-12-11 2:53 ` [PATCH v9 09/25] IB/umem: use get_user_pages_fast() to pin DMA pages John Hubbard
2019-12-11 2:53 ` [PATCH v9 10/25] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-12-11 20:57 ` Jonathan Corbet
2019-12-11 21:25 ` John Hubbard
2019-12-11 2:53 ` [PATCH v9 11/25] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-12-11 2:53 ` [PATCH v9 12/25] IB/{core,hw,umem}: set FOLL_PIN via pin_user_pages*(), fix up ODP John Hubbard
2019-12-11 2:53 ` [PATCH v9 13/25] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-12-11 2:53 ` [PATCH v9 14/25] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-12-11 2:53 ` [PATCH v9 15/25] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-12-11 2:53 ` [PATCH v9 16/25] net/xdp: " John Hubbard
2019-12-11 2:53 ` [PATCH v9 17/25] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-12-11 2:53 ` [PATCH v9 18/25] media/v4l2-core: pin_user_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-12-11 2:53 ` [PATCH v9 19/25] vfio, mm: " John Hubbard
2019-12-11 2:53 ` [PATCH v9 20/25] powerpc: book3s64: convert to pin_user_pages() and put_user_page() John Hubbard
2019-12-11 10:42 ` Jan Kara
2019-12-11 2:53 ` [PATCH v9 21/25] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1" John Hubbard
2019-12-11 2:53 ` [PATCH v9 22/25] mm, tree-wide: rename put_user_page*() to unpin_user_page*() John Hubbard
2019-12-11 2:53 ` [PATCH v9 23/25] mm/gup: track FOLL_PIN pages John Hubbard
2019-12-11 11:28 ` Jan Kara
2019-12-12 5:53 ` John Hubbard [this message]
2019-12-17 8:03 ` kbuild test robot
2019-12-17 8:03 ` [RFC PATCH] mm/gup: try_pin_compound_head() can be static kbuild test robot
2019-12-17 13:56 ` John Hubbard
2019-12-11 2:53 ` [PATCH v9 24/25] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-12-11 2:53 ` [PATCH v9 25/25] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=f961d0b6-c660-85b9-ad01-53bce74e39e9@nvidia.com \
--to=jhubbard@nvidia.com \
--cc=airlied@linux.ie \
--cc=akpm@linux-foundation.org \
--cc=alex.williamson@redhat.com \
--cc=axboe@kernel.dk \
--cc=benh@kernel.crashing.org \
--cc=bjorn.topel@intel.com \
--cc=bpf@vger.kernel.org \
--cc=corbet@lwn.net \
--cc=dan.j.williams@intel.com \
--cc=daniel@ffwll.ch \
--cc=davem@davemloft.net \
--cc=david@fromorbit.com \
--cc=dri-devel@lists.freedesktop.org \
--cc=hch@infradead.org \
--cc=ira.weiny@intel.com \
--cc=jack@suse.cz \
--cc=jgg@ziepe.ca \
--cc=jglisse@redhat.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=kvm@vger.kernel.org \
--cc=linux-block@vger.kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=linux-media@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-rdma@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=magnus.karlsson@intel.com \
--cc=mchehab@kernel.org \
--cc=mhocko@suse.com \
--cc=mike.kravetz@oracle.com \
--cc=mpe@ellerman.id.au \
--cc=netdev@vger.kernel.org \
--cc=paulus@samba.org \
--cc=shuah@kernel.org \
--cc=vbabka@suse.cz \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).