``void flush_dcache_page(struct page *page)``
- Any time the kernel writes to a page cache page, _OR_
- the kernel is about to read from a page cache page and
- user space shared/writable mappings of this page potentially
- exist, this routine is called.
+ This routines must be called when:
+
+ a) the kernel did write to a page that is in the page cache page
+ 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
+ on any page found in the user address space and thus driver
+ code rarely needs to take this into account.
.. note::
handling vfs symlinks in the page cache need not call
this interface at all.
- 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 flush here to handle
- D-cache aliasing, to make sure these kernel stores are
- visible to user space mappings of that page.
-
- The corollary case is just as important, if there are users
- which have shared+writable mappings of this file, we must make
- sure that kernel reads of these pages will see the most recent
- stores done by the user.
-
- 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 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 implementations for an example of how to go
- about doing this.
-
- The idea is, first at flush_dcache_page() time, if
- page->mapping->i_mmap is an empty tree, just mark the architecture
- private page flag bit. Later, in update_mmu_cache(), a check is
- made of this flag bit, and if set the flush is done and the flag
- bit is cleared.
+ 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
+ flush here to handle D-cache aliasing, to make sure these kernel stores
+ are visible to user space mappings of that page.
+
+ The corollary case is just as important, if there are users which have
+ shared+writable mappings of this file, we must make sure that kernel
+ reads of these pages will see the most recent stores done by the user.
+
+ 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
+ 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 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 mapping returns %false,
+ just mark the architecture private page flag bit. Later, in
+ update_mmu_cache(), a check is made of this flag bit, and if set the
+ flush is done and the flag bit is cleared.
.. important::
architectures). For incoherent architectures, it should flush
the cache of the page at vmaddr.
- ``void flush_kernel_dcache_page(struct page *page)``
-
- When the kernel needs to modify a user page is has obtained
- with kmap, it calls this function after all modifications are
- complete (but before kunmapping it) to bring the underlying
- page up to date. It is assumed here that the user has no
- incoherent cached copies (i.e. the original page was obtained
- from a mechanism like get_user_pages()). The default
- implementation is a nop and should remain so on all coherent
- architectures. On incoherent architectures, this should flush
- the kernel cache for page (using page_address(page)).
-
-
``void flush_icache_range(unsigned long start, unsigned long end)``
When the kernel stores into addresses that it will execute
projects / linux-2.6-microblaze.git / blobdiff