On Tue, Apr 10, 2018 at 03:47:28PM -0500, Christopher Lameter wrote:
> On Tue, 10 Apr 2018, Matthew Wilcox wrote:
>
> > In my continued attempt to clean up struct page, I've got to the point
> > where it'd be really nice to get rid of 'counters'. I like the patch
> > below because it makes it clear when & where we're doing "weird" things
> > to access the various counters.
>
> Well sounds good.
>
> > struct {
> > unsigned long flags;
> > union {
> > struct {
> > struct address_space *mapping;
> > pgoff_t index;
> > };
> > struct {
> > void *s_mem;
/* Dword boundary */
> > void *freelist;
> > };
> > ...
> > };
> > union {
> > atomic_t _mapcount;
> > unsigned int active;
>
> Is this aligned on a doubleword boundary? Maybe move the refcount below
> the flags field?
You need freelist and _mapcount to be in the same dword. There's no
space to put them both in dword 0, so that's used for flags and mapping
/ s_mem. Then freelist, mapcount and refcount are in dword 1 (on 64-bit),
or freelist & mapcount are in dword 1 on 32-bit. After that, 32 and 64-bit
no longer line up on the same dword boundaries.
