linux-kernel - Re: [PATCH 08/17] asm-generic/tlb: Provide MMU_GATHER_TABLE

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Date:   Thu, 12 Dec 2019 10:30:55 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will@...nel.org>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>
Cc:     linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Helge Deller <deller@....de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Paul Burton <paulburton@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Richard Henderson <rth@...ddle.net>,
        Nick Hu <nickhu@...estech.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [PATCH 08/17] asm-generic/tlb: Provide MMU_GATHER_TABLE_FREE

On Wed, Dec 11, 2019 at 01:07:21PM +0100, Peter Zijlstra wrote:
> @@ -56,6 +56,15 @@
>   *    Defaults to flushing at tlb_end_vma() to reset the range; helps when
>   *    there's large holes between the VMAs.
>   *
> + *  - tlb_remove_table()
> + *
> + *    tlb_remove_table() is the basic primitive to free page-table directories
> + *    (__p*_free_tlb()).  In it's most primitive form it is an alias for
> + *    tlb_remove_page() below, for when page directories are pages and have no
> + *    additional constraints.
> + *
> + *    See also MMU_GATHER_TABLE_FREE and MMU_GATHER_RCU_TABLE_FREE.
> + *
>   *  - tlb_remove_page() / __tlb_remove_page()
>   *  - tlb_remove_page_size() / __tlb_remove_page_size()
>   *

> @@ -202,7 +193,16 @@ struct mmu_table_batch {
>  
>  extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
>  
> -#endif
> +#else /* !CONFIG_MMU_GATHER_HAVE_TABLE_FREE */
> +
> +/*
> + * Without either HAVE_TABLE_FREE || CONFIG_HAVE_RCU_TABLE_FREE the
> + * architecture is assumed to have page based page directories and
> + * we can use the normal page batching to free them.
> + */
> +#define tlb_remove_table(tlb, page) tlb_remove_page((tlb), (page))
> +
> +#endif /* CONFIG_MMU_GATHER_TABLE_FREE */

The build robot kindly notified me that this breaks ARM because it does
the exact same #define for the same reason.

(and I noticed the comment is stale)

I'll post a new version of this patch with the below delta.

---
--- a/arch/arm/include/asm/tlb.h
+++ b/arch/arm/include/asm/tlb.h
@@ -37,10 +37,6 @@ static inline void __tlb_remove_table(vo
 
 #include <asm-generic/tlb.h>
 
-#ifndef CONFIG_MMU_GATHER_RCU_TABLE_FREE
-#define tlb_remove_table(tlb, entry) tlb_remove_page(tlb, entry)
-#endif
-
 static inline void
 __pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte, unsigned long addr)
 {
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -196,9 +196,8 @@ extern void tlb_remove_table(struct mmu_
 #else /* !CONFIG_MMU_GATHER_HAVE_TABLE_FREE */
 
 /*
- * Without either HAVE_TABLE_FREE || CONFIG_HAVE_RCU_TABLE_FREE the
- * architecture is assumed to have page based page directories and
- * we can use the normal page batching to free them.
+ * Without MMU_GATHER_TABLE_FREE the architecture is assumed to have page based
+ * page directories and we can use the normal page batching to free them.
  */
 #define tlb_remove_table(tlb, page) tlb_remove_page((tlb), (page))