Re: [PATCH v3 4/4] fs/sysv: Replace kmap() with kmap_local_page()

[Al Viro]

On Sat, Jan 21, 2023 at 12:05:58AM -0800, Ira Weiny wrote:

> First, arn't PAGE_ALIGN_DOWN(addr) and PTR_ALIGN_DOWN(addr, PAGE_SIZE) the
> same?
> 
> align.h
> #define PTR_ALIGN_DOWN(p, a)    ((typeof(p))ALIGN_DOWN((unsigned long)(p), (a)))
> 
> mm.h:
> #define PAGE_ALIGN_DOWN(addr) ALIGN_DOWN(addr, PAGE_SIZE)

... and ALIGN_DOWN ends up with doing bitwise and on the first argument.
Which doesn't work for pointers, thus the separate variant for those
and typecast to unsigned long in it...