On Fri, 21 Aug 2015, Andrew Morton wrote: > On Fri, 21 Aug 2015 22:31:09 +0300 "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> wrote: > > > On Fri, Aug 21, 2015 at 11:11:27AM -0500, Christoph Lameter wrote: > > > On Fri, 21 Aug 2015, Kirill A. Shutemov wrote: > > > > > > > > Is this really true? For example if it's a slab page, will that page > > > > > ever be inspected by code which is looking for the PageTail bit? > > > > > > > > +Christoph. > > > > > > > > What we know for sure is that space is not used in tail pages, otherwise > > > > it would collide with current compound_dtor. > > > > > > Sl*b allocators only do a virt_to_head_page on tail pages. > > > > The question was whether it's safe to assume that the bit 0 is always zero > > in the word as this bit will encode PageTail(). > > That wasn't my question actually... > > What I'm wondering is: if this page is being used for slab, will any > code path ever run PageTail() against it? If not, we don't need to be > concerned about that bit. virt_to_head_page will run PageTail because it uses compound_head(). And compound_head needs to use the first_page pointer if its a tail page. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>