From: Ira Weiny <ira.weiny@intel.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
John Hubbard <jhubbard@nvidia.com>,
Michal Hocko <mhocko@suse.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Jason Gunthorpe <jgg@ziepe.ca>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
"David S. Miller" <davem@davemloft.net>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Rich Felker <dalias@libc.org>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Ralf Baechle <ralf@linux-mips.org>,
James Hogan <jhogan@kernel.org>, linux-mm <linux-mm@kvack.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-mips@vger.kernel.org,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
linux-s390 <linux-s390@vger.kernel.org>,
Linux-sh <linux-sh@vger.kernel.org>,
sparclinux@vger.kernel.org, linux-rdma@vger.kernel.org,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: [RESEND 4/7] mm/gup: Add FOLL_LONGTERM capability to GUP fast
Date: Mon, 25 Mar 2019 01:42:26 -0700 [thread overview]
Message-ID: <20190325084225.GC16366@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <CAA9_cmcx-Bqo=CFuSj7Xcap3e5uaAot2reL2T74C47Ut6_KtQw@mail.gmail.com>
On Fri, Mar 22, 2019 at 03:12:55PM -0700, Dan Williams wrote:
> On Sun, Mar 17, 2019 at 7:36 PM <ira.weiny@intel.com> wrote:
> >
> > From: Ira Weiny <ira.weiny@intel.com>
> >
> > DAX pages were previously unprotected from longterm pins when users
> > called get_user_pages_fast().
> >
> > Use the new FOLL_LONGTERM flag to check for DEVMAP pages and fall
> > back to regular GUP processing if a DEVMAP page is encountered.
> >
> > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> > ---
> > mm/gup.c | 29 +++++++++++++++++++++++++----
> > 1 file changed, 25 insertions(+), 4 deletions(-)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 0684a9536207..173db0c44678 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1600,6 +1600,9 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
> > goto pte_unmap;
> >
> > if (pte_devmap(pte)) {
> > + if (unlikely(flags & FOLL_LONGTERM))
> > + goto pte_unmap;
> > +
> > pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
> > if (unlikely(!pgmap)) {
> > undo_dev_pagemap(nr, nr_start, pages);
> > @@ -1739,8 +1742,11 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
> > if (!pmd_access_permitted(orig, flags & FOLL_WRITE))
> > return 0;
> >
> > - if (pmd_devmap(orig))
> > + if (pmd_devmap(orig)) {
> > + if (unlikely(flags & FOLL_LONGTERM))
> > + return 0;
> > return __gup_device_huge_pmd(orig, pmdp, addr, end, pages, nr);
> > + }
> >
> > refs = 0;
> > page = pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> > @@ -1777,8 +1783,11 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
> > if (!pud_access_permitted(orig, flags & FOLL_WRITE))
> > return 0;
> >
> > - if (pud_devmap(orig))
> > + if (pud_devmap(orig)) {
> > + if (unlikely(flags & FOLL_LONGTERM))
> > + return 0;
> > return __gup_device_huge_pud(orig, pudp, addr, end, pages, nr);
> > + }
> >
> > refs = 0;
> > page = pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> > @@ -2066,8 +2075,20 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
> > start += nr << PAGE_SHIFT;
> > pages += nr;
> >
> > - ret = get_user_pages_unlocked(start, nr_pages - nr, pages,
> > - gup_flags);
> > + if (gup_flags & FOLL_LONGTERM) {
> > + down_read(¤t->mm->mmap_sem);
> > + ret = __gup_longterm_locked(current, current->mm,
> > + start, nr_pages - nr,
> > + pages, NULL, gup_flags);
> > + up_read(¤t->mm->mmap_sem);
> > + } else {
> > + /*
> > + * retain FAULT_FOLL_ALLOW_RETRY optimization if
> > + * possible
> > + */
> > + ret = get_user_pages_unlocked(start, nr_pages - nr,
> > + pages, gup_flags);
>
> I couldn't immediately grok why this path needs to branch on
> FOLL_LONGTERM? Won't get_user_pages_unlocked(..., FOLL_LONGTERM) do
> the right thing?
Unfortunately holding the lock is required to support FOLL_LONGTERM (to check
the VMAs) but we don't want to hold the lock to be optimal (specifically allow
FAULT_FOLL_ALLOW_RETRY). So I'm maintaining the optimization for *_fast users
who do not specify FOLL_LONGTERM.
Another way to do this would have been to define __gup_longterm_unlocked with
the above logic, but that seemed overkill at this point.
Ira
next prev parent reply other threads:[~2019-03-25 16:43 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-17 18:34 [RESEND PATCH 0/7] Add FOLL_LONGTERM to GUP fast and use it ira.weiny
2019-03-17 18:34 ` [RESEND 1/7] mm/gup: Replace get_user_pages_longterm() with FOLL_LONGTERM ira.weiny
2019-03-22 21:24 ` Dan Williams
2019-03-25 6:19 ` Ira Weiny
2019-03-25 16:45 ` Dan Williams
2019-03-25 8:46 ` Ira Weiny
2019-03-25 10:27 ` Ira Weiny
2019-03-17 18:34 ` [RESEND 2/7] mm/gup: Change write parameter to flags in fast walk ira.weiny
2019-03-22 21:30 ` Dan Williams
2019-03-17 18:34 ` [RESEND 3/7] mm/gup: Change GUP fast to use flags rather than a write 'bool' ira.weiny
2019-03-22 22:05 ` Dan Williams
2019-03-25 8:26 ` Ira Weiny
2019-03-17 18:34 ` [RESEND 4/7] mm/gup: Add FOLL_LONGTERM capability to GUP fast ira.weiny
2019-03-22 22:12 ` Dan Williams
2019-03-25 8:42 ` Ira Weiny [this message]
2019-03-25 16:47 ` Jason Gunthorpe
2019-03-25 9:23 ` Ira Weiny
2019-03-25 17:51 ` Jason Gunthorpe
2019-03-25 14:21 ` Ira Weiny
2019-03-25 22:36 ` Dan Williams
2019-03-25 14:54 ` Ira Weiny
2019-03-17 18:34 ` [RESEND 5/7] IB/hfi1: Use the new FOLL_LONGTERM flag to get_user_pages_fast() ira.weiny
2019-03-22 22:14 ` Dan Williams
2019-03-25 8:43 ` Ira Weiny
2019-03-17 18:34 ` [RESEND 6/7] IB/qib: " ira.weiny
2019-03-22 22:15 ` Dan Williams
2019-03-17 18:34 ` [RESEND 7/7] IB/mthca: " ira.weiny
2019-03-19 22:19 ` [RESEND PATCH 0/7] Add FOLL_LONGTERM to GUP fast and use it Andrew Morton
2019-03-21 8:40 ` Ira Weiny
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