On Thu, Apr 21, 2022 at 08:01:59PM +0200, Fabio M. De Francesco wrote: > The use of kmap_atomic() is deprecated in favor of kmap_local_page(). I'm not sure deprecated is the right word. And I think the fact that this documentation is stale is a better reason for the patch as is. This series should end up indicating the desire to stop growing kmap() and kmap_atomic() call sites and that their deprecation is on the horizon. I've not read the text in patch 4/4 yet. > For > this reason the "Using kmap_atomic" section in highmem.rst is obsolete and > unnecessary. A lot of the text is obsolete (and redundant) but the example code might be useful. Why not move the example and relevant bits into the kdoc for kmap_atomic() which is then automatically picked up via patch 2/4. Ira > > Therefore, just remove it. > > 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 | 35 ----------------------------------- > 1 file changed, 35 deletions(-) > > diff --git a/Documentation/vm/highmem.rst b/Documentation/vm/highmem.rst > index ccff08a8211d..e05bf5524174 100644 > --- a/Documentation/vm/highmem.rst > +++ b/Documentation/vm/highmem.rst > @@ -72,41 +72,6 @@ The kernel contains several ways of creating temporary mappings: > It may be assumed that k[un]map_atomic() won't fail. > > > -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 > ========================== > > -- > 2.34.1 >
