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Message-ID: <b300037e-0d9d-db60-49dd-858d8a872355@arm.com>
Date: Thu, 25 May 2023 08:13:12 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
linux-arch@...r.kernel.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 04/36] mm: Remove ARCH_IMPLEMENTS_FLUSH_DCACHE_FOLIO
On 3/15/23 10:44, Matthew Wilcox (Oracle) wrote:
> Current best practice is to reuse the name of the function as a define
> to indicate that the function is implemented by the architecture.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
> Documentation/core-api/cachetlb.rst | 24 +++++++++---------------
> include/linux/cacheflush.h | 4 ++--
> mm/util.c | 2 +-
> 3 files changed, 12 insertions(+), 18 deletions(-)
>
> diff --git a/Documentation/core-api/cachetlb.rst b/Documentation/core-api/cachetlb.rst
> index d4c9e2a28d36..770008afd409 100644
> --- a/Documentation/core-api/cachetlb.rst
> +++ b/Documentation/core-api/cachetlb.rst
> @@ -269,7 +269,7 @@ maps this page at its virtual address.
> If D-cache aliasing is not an issue, these two routines may
> simply call memcpy/memset directly and do nothing more.
>
> - ``void flush_dcache_page(struct page *page)``
> + ``void flush_dcache_folio(struct folio *folio)``
>
> This routines must be called when:
>
> @@ -277,7 +277,7 @@ maps this page at its virtual address.
> and / or in high memory
> b) the kernel is about to read from a page cache page and user space
> shared/writable mappings of this page potentially exist. Note
> - that {get,pin}_user_pages{_fast} already call flush_dcache_page
> + that {get,pin}_user_pages{_fast} already call flush_dcache_folio
> on any page found in the user address space and thus driver
> code rarely needs to take this into account.
>
> @@ -291,7 +291,7 @@ maps this page at its virtual address.
>
> The phrase "kernel writes to a page cache page" means, specifically,
> that the kernel executes store instructions that dirty data in that
> - page at the page->virtual mapping of that page. It is important to
> + page at the kernel virtual mapping of that page. It is important to
> flush here to handle D-cache aliasing, to make sure these kernel stores
> are visible to user space mappings of that page.
>
> @@ -302,18 +302,18 @@ maps this page at its virtual address.
> If D-cache aliasing is not an issue, this routine may simply be defined
> as a nop on that architecture.
>
> - There is a bit set aside in page->flags (PG_arch_1) as "architecture
> + There is a bit set aside in folio->flags (PG_arch_1) as "architecture
> private". The kernel guarantees that, for pagecache pages, it will
> clear this bit when such a page first enters the pagecache.
>
> This allows these interfaces to be implemented much more
> efficiently. It allows one to "defer" (perhaps indefinitely) the
> actual flush if there are currently no user processes mapping this
> - page. See sparc64's flush_dcache_page and update_mmu_cache_range
> + page. See sparc64's flush_dcache_folio and update_mmu_cache_range
> implementations for an example of how to go about doing this.
>
> - The idea is, first at flush_dcache_page() time, if
> - page_file_mapping() returns a mapping, and mapping_mapped on that
> + The idea is, first at flush_dcache_folio() time, if
> + folio_flush_mapping() returns a mapping, and mapping_mapped() on that
> mapping returns %false, just mark the architecture private page
> flag bit. Later, in update_mmu_cache_range(), a check is made
> of this flag bit, and if set the flush is done and the flag bit
> @@ -327,12 +327,6 @@ maps this page at its virtual address.
> dirty. Again, see sparc64 for examples of how
> to deal with this.
>
> - ``void flush_dcache_folio(struct folio *folio)``
> - This function is called under the same circumstances as
> - flush_dcache_page(). It allows the architecture to
> - optimise for flushing the entire folio of pages instead
> - of flushing one page at a time.
> -
> ``void copy_to_user_page(struct vm_area_struct *vma, struct page *page,
> unsigned long user_vaddr, void *dst, void *src, int len)``
> ``void copy_from_user_page(struct vm_area_struct *vma, struct page *page,
> @@ -353,7 +347,7 @@ maps this page at its virtual address.
>
> When the kernel needs to access the contents of an anonymous
> page, it calls this function (currently only
> - get_user_pages()). Note: flush_dcache_page() deliberately
> + get_user_pages()). Note: flush_dcache_folio() deliberately
> doesn't work for an anonymous page. The default
> implementation is a nop (and should remain so for all coherent
> architectures). For incoherent architectures, it should flush
> @@ -370,7 +364,7 @@ maps this page at its virtual address.
> ``void flush_icache_page(struct vm_area_struct *vma, struct page *page)``
>
> All the functionality of flush_icache_page can be implemented in
> - flush_dcache_page and update_mmu_cache_range. In the future, the hope
> + flush_dcache_folio and update_mmu_cache_range. In the future, the hope
> is to remove this interface completely.
>
> The final category of APIs is for I/O to deliberately aliased address
> diff --git a/include/linux/cacheflush.h b/include/linux/cacheflush.h
> index a6189d21f2ba..82136f3fcf54 100644
> --- a/include/linux/cacheflush.h
> +++ b/include/linux/cacheflush.h
> @@ -7,14 +7,14 @@
> struct folio;
>
> #if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
> -#ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_FOLIO
> +#ifndef flush_dcache_folio
> void flush_dcache_folio(struct folio *folio);
> #endif
> #else
> static inline void flush_dcache_folio(struct folio *folio)
> {
> }
> -#define ARCH_IMPLEMENTS_FLUSH_DCACHE_FOLIO 0
> +#define flush_dcache_folio flush_dcache_folio
> #endif /* ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE */
>
> #endif /* _LINUX_CACHEFLUSH_H */
> diff --git a/mm/util.c b/mm/util.c
> index dd12b9531ac4..98ce51b01627 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -1125,7 +1125,7 @@ void page_offline_end(void)
> }
> EXPORT_SYMBOL(page_offline_end);
>
> -#ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_FOLIO
> +#ifndef flush_dcache_folio
> void flush_dcache_folio(struct folio *folio)
> {
> long i, nr = folio_nr_pages(folio);
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