linux-kernel - Re: [PATCH 4/4] powerpc/mm/radix: Implement tlb mmu gather flush efficiently

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Message-Id: <20160602131250.e4d43401e7eade277bc4476a@linux-foundation.org>
Date:	Thu, 2 Jun 2016 13:12:50 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	mpe@...erman.id.au, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 4/4] powerpc/mm/radix: Implement tlb mmu gather flush
 efficiently

On Thu,  2 Jun 2016 15:09:49 +0530 "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:

> Now that we track page size in mmu_gather, we can use address based
> tlbie format when doing a tlb_flush(). We don't do this if we are
> invalidating the full address space.
> 
> ...
>
>  void radix__tlb_flush(struct mmu_gather *tlb)
>  {
> +	int psize = 0;
>  	struct mm_struct *mm = tlb->mm;
> -	radix__flush_tlb_mm(mm);
> +	int page_size = tlb->page_size;
> +
> +	psize = radix_get_mmu_psize(page_size);
> +	if (psize == -1)
> +		/* unknown page size */
> +		goto flush_mm;
> +
> +	if (!tlb->fullmm && !tlb->need_flush_all)
> +		radix__flush_tlb_range_psize(mm, tlb->start, tlb->end, psize);
> +	else
> +flush_mm:
> +		radix__flush_tlb_mm(mm);

That's kinda ugly.  What about

void radix__tlb_flush(struct mmu_gather *tlb)
{
	int psize = 0;
	struct mm_struct *mm = tlb->mm;
	int page_size = tlb->page_size;

	psize = radix_get_mmu_psize(page_size);

	if (psize != -1 && !tlb->fullmm && !tlb->need_flush_all)
		radix__flush_tlb_range_psize(mm, tlb->start, tlb->end, psize);
	else
		radix__flush_tlb_mm(mm);
}

?

We lost the comment, but that can be neatly addressed by documenting
radix_get_mmu_psize() (of course!).  Please send along a comment to do
this and I'll add it in.

--- a/arch/powerpc/mm/tlb-radix.c~powerpc-mm-radix-implement-tlb-mmu-gather-flush-efficiently-fix
+++ a/arch/powerpc/mm/tlb-radix.c
@@ -265,13 +265,9 @@ void radix__tlb_flush(struct mmu_gather
 	int page_size = tlb->page_size;
 
 	psize = radix_get_mmu_psize(page_size);
-	if (psize == -1)
-		/* unknown page size */
-		goto flush_mm;
 
-	if (!tlb->fullmm && !tlb->need_flush_all)
+	if (psize != -1 && !tlb->fullmm && !tlb->need_flush_all)
 		radix__flush_tlb_range_psize(mm, tlb->start, tlb->end, psize);
 	else
-flush_mm:
 		radix__flush_tlb_mm(mm);
 }
_

I'll await feedback from the other PPC developers before doing anything
further on this patchset.

hm, no ppc mailing lists were cc'ed.  Regrettable.