On Wed, May 16, 2007 at 12:47:54PM -0700, Linus Torvalds wrote: > > On Wed, 16 May 2007, Hugh Dickins wrote: > > > > The other option of moving the bit into ->mapping hopefully avoids all > > > the issues, and would probably be a little faster again on the P4, at the > > > expense of being a more intrusive (but it doesn't look too bad, at first > > > glance)... > > > > Hmm, I'm so happy with PG_swapcache in there, that I'm reluctant to > > cede it to your PG_locked, though I can't deny your use should take > > precedence. Perhaps we could enforce 8-byte alignment of struct > > address_space and struct anon_vma to make both bits available > > (along with the anon bit). > > We probably could. It should be easy enough to mark "struct address_space" > to be 8-byte aligned.
Yeah, it might be worthwhile, because I agree that PG_swapcache would work nicely there too. > > But I think you may not be appreciating how intrusive PG_locked > > will be. There are many references to page->mapping (often ->host) > > throughout fs/ : when we keep anon/swap flags in page->mapping, we > > know the filesystems will never see those bits set in their pages, > > so no page_mapping-like conversion is needed; just a few places in > > common code need to adapt. > > You're right, it could be really painful. We'd have to rename the field, > and use some inline function to access it (which masks off the low bits). Yeah, I realise that the change is intrusive in terms of lines touched, but AFAIKS, it should not be much more complex than a search/replace... As far as deprecating things goes... I don't think we have to wait too long, its more for features, drivers, or more fundamental APIs isn't it? If we just point out that one must use set_page_mapping/page_mapping rather than page->mapping, it is trivial to fix any out of tree breakage. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
