Re: [PATCH -next 0/3] Add support for fast mremap

[Joel Fernandes <joel@joelfernandes.org>]

On Sat, Nov 03, 2018 at 09:24:05AM +0000, Anton Ivanov wrote:
> On 03/11/2018 09:15, Richard Weinberger wrote:
> > Joel,
> > 
> > Am Samstag, 3. November 2018, 05:00:38 CET schrieb Joel Fernandes:
> > > Hi,
> > > Here is the latest "fast mremap" series. This just a repost with Kirill's
> > > Acked-bys added. I would like this to be considered for linux -next.  I also
> > > dropped the CONFIG enablement patch for arm64 since I am yet to test it with
> > > the new TLB flushing code that is in very recent kernel releases. (None of my
> > > arm64 devices run mainline right now.) so I will post the arm64 enablement once
> > > I get to that. The performance numbers in the series are for x86.
> > > 
> > > List of patches in series:
> > > 
> > > (1) mm: select HAVE_MOVE_PMD in x86 for faster mremap
> > > 
> > > (2) mm: speed up mremap by 20x on large regions (v4)
> > > v1->v2: Added support for per-arch enablement (Kirill Shutemov)
> > > v2->v3: Updated commit message to state the optimization may also
> > > 	run for non-thp type of systems (Daniel Col).
> > > v3->v4: Remove useless pmd_lock check (Kirill Shutemov)
> > > 	Rebased ontop of Linus's master, updated perf results based
> > >          on x86 testing. Added Kirill's Acks.
> > > 
> > > (3) mm: treewide: remove unused address argument from pte_alloc functions (v2)
> > > v1->v2: fix arch/um/ prototype which was missed in v1 (Anton Ivanov)
> > >          update changelog with manual fixups for m68k and microblaze.
> > > 
> > > not included - (4) mm: select HAVE_MOVE_PMD in arm64 for faster mremap
> > >      This patch is dropped since last posting pending further performance
> > >      testing on arm64 with new TLB gather updates. See notes in patch
> > >      titled "mm: speed up mremap by 500x on large regions" for more
> > >      details.
> > > 
> > This breaks UML build:
> >    CC      mm/mremap.o
> > mm/mremap.c: In function ‘move_normal_pmd’:
> > mm/mremap.c:229:2: error: implicit declaration of function ‘set_pmd_at’; did you mean ‘set_pte_at’? [-Werror=implicit-function-declaration]
> >    set_pmd_at(mm, new_addr, new_pmd, pmd);
> >    ^~~~~~~~~~
> >    set_pte_at
> >    CC      crypto/rng.o
> >    CC      fs/direct-io.o
> > cc1: some warnings being treated as errors
> > 
> > To test yourself, just run on a x86 box:
> > $ make defconfig ARCH=um
> > $ make linux ARCH=um
> > 
> > Thanks,
> > //richard
> > 
> > 
> > 
> 
> UM somehow managed to miss one of the 3-level functions, I sent a patch at
> some point to add to the mmremap series, but it looks like it did not get
> included in the final version.
> 
> You need these two incremental on top of Joel's patch. Richard - feel free
> to relocate the actual implementation of the set_pgd_at elsewhere - I put it
> at the end of tlb.c
> 
> diff --git a/arch/um/include/asm/pgtable.h b/arch/um/include/asm/pgtable.h
> index 7485398d0737..1692da55e63a 100644
> --- a/arch/um/include/asm/pgtable.h
> +++ b/arch/um/include/asm/pgtable.h
> @@ -359,4 +359,7 @@ do {                                                \
>         __flush_tlb_one((vaddr));               \
>  } while (0)
> 
> +extern void set_pmd_at(struct mm_struct *mm, unsigned long addr,
> +               pmd_t *pmdp, pmd_t pmd);
> +
>  #endif
> diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c
> index 763d35bdda01..d17b74184ba0 100644
> --- a/arch/um/kernel/tlb.c
> +++ b/arch/um/kernel/tlb.c
> @@ -647,3 +647,9 @@ void force_flush_all(void)
>                 vma = vma->vm_next;
>         }
>  }
> +void set_pmd_at(struct mm_struct *mm, unsigned long addr,
> +               pmd_t *pmdp, pmd_t pmd)
> +{
> +       *pmdp = pmd;
> +}
> +
> 

Looks like more architectures don't define set_pmd_at. I am thinking the
easiest way forward is to just do the following, instead of defining
set_pmd_at for every architecture that doesn't care about it. Thoughts?

diff --git a/mm/mremap.c b/mm/mremap.c
index 7cf6b0943090..31ad64dcdae6 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -281,7 +281,8 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 			split_huge_pmd(vma, old_pmd, old_addr);
 			if (pmd_trans_unstable(old_pmd))
 				continue;
-		} else if (extent == PMD_SIZE && IS_ENABLED(CONFIG_HAVE_MOVE_PMD)) {
+		} else if (extent == PMD_SIZE) {
+#ifdef CONFIG_HAVE_MOVE_PMD
 			/*
 			 * If the extent is PMD-sized, try to speed the move by
 			 * moving at the PMD level if possible.
@@ -296,6 +297,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 				drop_rmap_locks(vma);
 			if (moved)
 				continue;
+#endif
 		}
 
 		if (pte_alloc(new_vma->vm_mm, new_pmd))