Messages in this thread Patch in this message | | | Date | Thu, 14 May 2015 18:07:48 +0200 | From | Vlastimil Babka <> | Subject | Re: [PATCHv5 02/28] rmap: add argument to charge compound page |
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On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote: > We're going to allow mapping of individual 4k pages of THP compound > page. It means we cannot rely on PageTransHuge() check to decide if > map/unmap small page or THP. > > The patch adds new argument to rmap functions to indicate whether we want > to operate on whole compound page or only the small page. > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Tested-by: Sasha Levin <sasha.levin@oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
But I wonder about one thing:
> -void page_remove_rmap(struct page *page) > +void page_remove_rmap(struct page *page, bool compound) > { > + int nr = compound ? hpage_nr_pages(page) : 1; > + > if (!PageAnon(page)) { > + VM_BUG_ON_PAGE(compound && !PageHuge(page), page); > page_remove_file_rmap(page); > return; > }
The function continues by:
/* page still mapped by someone else? */ if (!atomic_add_negative(-1, &page->_mapcount)) return;
/* Hugepages are not counted in NR_ANON_PAGES for now. */ if (unlikely(PageHuge(page))) return;
The handling of compound parameter for PageHuge() pages feels just weird. You use hpage_nr_pages() for them which tests PageTransHuge(). It doesn't break anything and the value of nr is effectively ignored anyway, but still...
So I wonder, if all callers of page_remove_rmap() for PageHuge() pages are the two in mm/hugetlb.c, why not just create a special case function? Or are some callers elsewhere, not aware whether they are calling this on a PageHuge()? So compound might be even false for those? If that's all possible and legal, then maybe explain it in a comment to reduce confusion of further readers. And move the 'nr' assignment to a place where we are sure it's not a PageHuge(), i.e. right above the place the value is used, perhaps?
> @@ -1181,11 +1191,12 @@ void page_remove_rmap(struct page *page) > * these counters are not modified in interrupt context, and > * pte lock(a spinlock) is held, which implies preemption disabled. > */ > - if (PageTransHuge(page)) > + if (compound) { > + VM_BUG_ON_PAGE(!PageTransHuge(page), page); > __dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES); > + } > > - __mod_zone_page_state(page_zone(page), NR_ANON_PAGES, > - -hpage_nr_pages(page)); > + __mod_zone_page_state(page_zone(page), NR_ANON_PAGES, -nr); > > if (unlikely(PageMlocked(page))) > clear_page_mlock(page); > @@ -1327,7 +1338,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, > dec_mm_counter(mm, MM_FILEPAGES); > > discard: > - page_remove_rmap(page); > + page_remove_rmap(page, false); > page_cache_release(page); > > out_unmap:
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