lkml.org 
[lkml]   [2019]   [Apr]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH 1/9] mm: Allow the [page|pfn]_mkwrite callbacks to drop the mmap_sem
On Wed, Apr 17, 2019 at 4:28 PM Thomas Hellstrom <thellstrom@vmware.com> wrote:
>
> Hi, Souptick,
>
> On Sat, 2019-04-13 at 20:41 +0530, Souptick Joarder wrote:
> > On Fri, Apr 12, 2019 at 9:34 PM Thomas Hellstrom <
> > thellstrom@vmware.com> wrote:
> > > Driver fault callbacks are allowed to drop the mmap_sem when
> > > expecting
> > > long hardware waits to avoid blocking other mm users. Allow the
> > > mkwrite
> > > callbacks to do the same by returning early on VM_FAULT_RETRY.
> > >
> > > In particular we want to be able to drop the mmap_sem when waiting
> > > for
> > > a reservation object lock on a GPU buffer object. These locks may
> > > be
> > > held while waiting for the GPU.
> > >
> > > Cc: Andrew Morton <akpm@linux-foundation.org>
> > > Cc: Matthew Wilcox <willy@infradead.org>
> > > Cc: Will Deacon <will.deacon@arm.com>
> > > Cc: Peter Zijlstra <peterz@infradead.org>
> > > Cc: Rik van Riel <riel@surriel.com>
> > > Cc: Minchan Kim <minchan@kernel.org>
> > > Cc: Michal Hocko <mhocko@suse.com>
> > > Cc: Huang Ying <ying.huang@intel.com>
> > > Cc: Souptick Joarder <jrdr.linux@gmail.com>
> > > Cc: "Jérôme Glisse" <jglisse@redhat.com>
> > > Cc: linux-mm@kvack.org
> > > Cc: linux-kernel@vger.kernel.org
> > >
> > > Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
> > > ---
> > > mm/memory.c | 10 ++++++----
> > > 1 file changed, 6 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/mm/memory.c b/mm/memory.c
> > > index e11ca9dd823f..a95b4a3b1ae2 100644
> > > --- a/mm/memory.c
> > > +++ b/mm/memory.c
> > > @@ -2144,7 +2144,7 @@ static vm_fault_t do_page_mkwrite(struct
> > > vm_fault *vmf)
> > > ret = vmf->vma->vm_ops->page_mkwrite(vmf);
> > > /* Restore original flags so that caller is not surprised
> > > */
> > > vmf->flags = old_flags;
> > > - if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
> > > + if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_RETRY |
> > > VM_FAULT_NOPAGE)))
> >
> > With this patch there will multiple instances of (VM_FAULT_ERROR |
> > VM_FAULT_RETRY | VM_FAULT_NOPAGE)
> > in mm/memory.c. Does it make sense to wrap it in a macro and use it ?
>
> Even though the code will look neater, it might be trickier to follow a
> particular error path. Could we perhaps postpone to a follow-up patch?

Sure. follow-up-patch is fine.

>
> Thomas
>
>
>
> >
> > > return ret;
> > > if (unlikely(!(ret & VM_FAULT_LOCKED))) {
> > > lock_page(page);
> > > @@ -2419,7 +2419,7 @@ static vm_fault_t wp_pfn_shared(struct
> > > vm_fault *vmf)
> > > pte_unmap_unlock(vmf->pte, vmf->ptl);
> > > vmf->flags |= FAULT_FLAG_MKWRITE;
> > > ret = vma->vm_ops->pfn_mkwrite(vmf);
> > > - if (ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))
> > > + if (ret & (VM_FAULT_ERROR | VM_FAULT_RETRY |
> > > VM_FAULT_NOPAGE))
> > > return ret;
> > > return finish_mkwrite_fault(vmf);
> > > }
> > > @@ -2440,7 +2440,8 @@ static vm_fault_t wp_page_shared(struct
> > > vm_fault *vmf)
> > > pte_unmap_unlock(vmf->pte, vmf->ptl);
> > > tmp = do_page_mkwrite(vmf);
> > > if (unlikely(!tmp || (tmp &
> > > - (VM_FAULT_ERROR |
> > > VM_FAULT_NOPAGE)))) {
> > > + (VM_FAULT_ERROR |
> > > VM_FAULT_RETRY |
> > > + VM_FAULT_NOPAGE)))) {
> > > put_page(vmf->page);
> > > return tmp;
> > > }
> > > @@ -3494,7 +3495,8 @@ static vm_fault_t do_shared_fault(struct
> > > vm_fault *vmf)
> > > unlock_page(vmf->page);
> > > tmp = do_page_mkwrite(vmf);
> > > if (unlikely(!tmp ||
> > > - (tmp & (VM_FAULT_ERROR |
> > > VM_FAULT_NOPAGE)))) {
> > > + (tmp & (VM_FAULT_ERROR |
> > > VM_FAULT_RETRY |
> > > + VM_FAULT_NOPAGE)))) {
> > > put_page(vmf->page);
> > > return tmp;
> > > }
> > > --
> > > 2.20.1
> > >

\
 
 \ /
  Last update: 2019-04-17 15:01    [W:0.071 / U:2.436 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site