Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ira Weiny <ira.weiny@xxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx> --- Documentation/vm/highmem.rst | 41 ++++++------------------------------ 1 file changed, 6 insertions(+), 35 deletions(-) diff --git a/Documentation/vm/highmem.rst b/Documentation/vm/highmem.rst index 12dcfbee094d..5dcee6233cd5 100644 --- a/Documentation/vm/highmem.rst +++ b/Documentation/vm/highmem.rst @@ -117,41 +117,6 @@ The kernel contains several ways of creating temporary mappings: synchronization to unmap. -Using kmap_atomic -================= - -When and where to use kmap_atomic() is straightforward. It is used when code -wants to access the contents of a page that might be allocated from high memory -(see __GFP_HIGHMEM), for example a page in the pagecache. The API has two -functions, and they can be used in a manner similar to the following:: - - /* Find the page of interest. */ - struct page *page = find_get_page(mapping, offset); - - /* Gain access to the contents of that page. */ - void *vaddr = kmap_atomic(page); - - /* Do something to the contents of that page. */ - memset(vaddr, 0, PAGE_SIZE); - - /* Unmap that page. */ - kunmap_atomic(vaddr); - -Note that the kunmap_atomic() call takes the result of the kmap_atomic() call -not the argument. - -If you need to map two pages because you want to copy from one page to -another you need to keep the kmap_atomic calls strictly nested, like:: - - vaddr1 = kmap_atomic(page1); - vaddr2 = kmap_atomic(page2); - - memcpy(vaddr1, vaddr2, PAGE_SIZE); - - kunmap_atomic(vaddr2); - kunmap_atomic(vaddr1); - - Cost of Temporary Mappings ========================== @@ -190,3 +155,9 @@ The general recommendation is that you don't use more than 8GiB on a 32-bit machine - although more might work for you and your workload, you're pretty much on your own - don't expect kernel developers to really care much if things come apart. + + +Functions +========= + +.. kernel-doc:: include/linux/highmem.h -- 2.34.1
