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mm: clarify why we avoid page_mapcount() for slab pages in dump_page()

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Let's add comment on why we skip page_mapcount() for sl[aou]b pages.

Link: http://lkml.kernel.org/r/20160922105532.GB24593@node
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kirill A. Shutemov 2016-10-07 17:01:40 -07:00 committed by Linus Torvalds
parent 8f26e0b176
commit 9996f05eac
1 changed files with 5 additions and 0 deletions
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5
mm/debug.c
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@ -42,6 +42,11 @@ const struct trace_print_flags vmaflag_names[] = {
void __dump_page(struct page *page, const char *reason)
{
/*
* Avoid VM_BUG_ON() in page_mapcount().
* page->_mapcount space in struct page is used by sl[aou]b pages to
* encode own info.
*/
int mapcount = PageSlab(page) ? 0 : page_mapcount(page);
pr_emerg("page:%p count:%d mapcount:%d mapping:%p index:%#lx",