From: Souptick Joarder <jrdr.linux@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Russell King - ARM Linux <linux@armlinux.org.uk>,
Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
robin@protonic.nl, stefanr@s5r6.in-berlin.de, hjc@rock-chips.com,
Heiko Stuebner <heiko@sntech.de>,
airlied@linux.ie, robin.murphy@arm.com, iamjoonsoo.kim@lge.com,
Andrew Morton <akpm@linux-foundation.org>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Kees Cook <keescook@chromium.org>,
treding@nvidia.com, Michal Hocko <mhocko@suse.com>,
Dan Williams <dan.j.williams@intel.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Mark Rutland <mark.rutland@arm.com>,
aryabinin@virtuozzo.com, Dmitry Vyukov <dvyukov@google.com>,
Kate Stewart <kstewart@linuxfoundation.org>,
tchibo@google.com, riel@redhat.com,
Minchan Kim <minchan@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
"Huang, Ying" <ying.huang@intel.com>,
ak@linux.intel.com, rppt@linux.vnet.ibm.com,
linux@dominikbrodowski.net, Arnd Bergmann <arnd@arndb.de>,
cpandya@codeaurora.org, hannes@cmpxchg.org,
Joe Perches <joe@perches.com>,
mcgrof@kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
linux1394-devel@lists.sourceforge.net,
dri-devel@lists.freedesktop.org,
linux-rockchip@lists.infradead.org, Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH v2] mm: Introduce new function vm_insert_kmem_page
Date: Fri, 5 Oct 2018 00:23:07 +0530 [thread overview]
Message-ID: <CAFqt6zaN0PQHkjuwFf8VriROLy7qrPDu-iNE=VPiXJw8C7GpQg@mail.gmail.com> (raw)
In-Reply-To: <20181004181736.GB20842@bombadil.infradead.org>
On Thu, Oct 4, 2018 at 11:47 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Thu, Oct 04, 2018 at 11:42:18PM +0530, Souptick Joarder wrote:
> > On Thu, Oct 4, 2018 at 6:04 PM Russell King - ARM Linux
> > <linux@armlinux.org.uk> wrote:
> > > I'm confused, what are you trying to do?
> > >
> > > It seems that we already have:
> > >
> > > vm_insert_page() - returns an errno
> > > vmf_insert_page() - returns a VM_FAULT_* code
> > >
> > > From what I _think_ you're saying, you're trying to provide
> > > vm_insert_kmem_page() as a direct replacement for the existing
> > > vm_insert_page(), and then make vm_insert_page() behave as per
> > > vmf_insert_page(), so we end up with:
> >
> > yes, vm_insert_kmem_page() can be a direct replacement of vm_insert_page
> > or might be a wrapper function written using vm_insert_page whichever
> > suites better
> > based on feedback.
> >
> > >
> > > vm_insert_kmem_page() - returns an errno
> > > vm_insert_page() - returns a VM_FAULT_* code
> > > vmf_insert_page() - returns a VM_FAULT_* code and is identical to
> > > vm_insert_page()
> > >
> >
> > After completion of conversion we end up with
> >
> > vm_insert_kmem_page() - returns an errno
> > vmf_insert_page() - returns a VM_FAULT_* code
> >
> >
> > > Given that the documentation for vm_insert_page() says:
> > >
> > > * Usually this function is called from f_op->mmap() handler
> > > * under mm->mmap_sem write-lock, so it can change vma->vm_flags.
> > > * Caller must set VM_MIXEDMAP on vma if it wants to call this
> > > * function from other places, for example from page-fault handler.
> > >
> > > this says that the "usual" use method for vm_insert_page() is
> > > _outside_ of page fault handling - if it is used _inside_ page fault
> > > handling, then it states that additional fixups are required on the
> > > VMA. So I don't get why your patch commentry seems to be saying that
> > > users of vm_insert_page() outside of page fault handling all need to
> > > be patched - isn't this the use case that this function is defined
> > > to be handling?
> >
> > The answer is yes best of my knowledge.
> >
> > But as mentioned in change log ->
> >
> > Going forward, the plan is to restrict future drivers not
> > to use vm_insert_page ( *it will generate new errno to
> > VM_FAULT_CODE mapping code for new drivers which were already
> > cleaned up for existing drivers*) in #PF (page fault handler)
> > context but to make use of vmf_insert_page which returns
> > VMF_FAULT_CODE and that is not possible until both vm_insert_page
> > and vmf_insert_page API exists.
> >
> > But there are some consumers of vm_insert_page which use it
> > outside #PF context. straight forward conversion of vm_insert_page
> > to vmf_insert_page won't work there as those function calls expects
> > errno not vm_fault_t in return.
> >
> > If both {vm, vmf}_insert_page exists, vm_insert_page might be used for
> > #PF context which we want to protect by removing/ replacing vm_insert_page
> > with another similar/ wrapper API.
> >
> > Is that the right answer of your question ? no ?
>
> I think this is a bad plan. What we should rather do is examine the current
> users of vm_insert_page() and ask "What interface would better replace
> vm_insert_page()?"
>
> As I've said to you before, I believe the right answer is to have a
> vm_insert_range() which takes an array of struct page pointers. That
> fits the majority of remaining users.
Ok, but it will take some time.
Is it a good idea to introduce the final vm_fault_t patch and then
start working on vm_insert_range as it will be bit time consuming ?
>
> ----
>
> If we do want to rename vm_insert_page() to vm_insert_kmem_page(), then
> the right answer is to _just do that_. Not duplicate vm_insert_page()
> in its entirety. I don't see the point to doing that.
next prev parent reply other threads:[~2018-10-04 18:50 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-03 18:58 [PATCH v2] mm: Introduce new function vm_insert_kmem_page Souptick Joarder
2018-10-03 19:58 ` Miguel Ojeda
2018-10-04 11:56 ` Souptick Joarder
2018-10-03 20:00 ` Matthew Wilcox
2018-10-03 22:14 ` Russell King - ARM Linux
2018-10-04 0:39 ` Matthew Wilcox
2018-10-04 12:15 ` Souptick Joarder
2018-10-04 12:34 ` Russell King - ARM Linux
2018-10-04 18:12 ` Souptick Joarder
2018-10-04 18:17 ` Matthew Wilcox
2018-10-04 18:53 ` Souptick Joarder [this message]
2018-10-04 19:46 ` Miguel Ojeda
2018-10-05 5:50 ` Souptick Joarder
2018-10-05 8:52 ` Miguel Ojeda
2018-10-05 10:01 ` Souptick Joarder
2018-10-05 10:49 ` Miguel Ojeda
2018-10-05 12:11 ` Souptick Joarder
2018-10-05 18:09 ` Miguel Ojeda
2018-10-06 5:14 ` Souptick Joarder
2018-10-06 10:49 ` Miguel Ojeda
2018-10-23 12:14 ` Souptick Joarder
2018-10-23 12:24 ` Matthew Wilcox
2018-10-23 12:33 ` Souptick Joarder
2018-10-23 12:59 ` Matthew Wilcox
2018-10-23 13:15 ` Souptick Joarder
2018-10-04 18:21 ` Souptick Joarder
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