On Sat, 26 Sep 2015 13:45:53 +0300 Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> wrote: > Currently, to charge a page to kmemcg one should use alloc_kmem_pages > helper. When the page is not needed anymore it must be freed with > free_kmem_pages helper, which will uncharge the page before freeing it. > Such a design is acceptable for thread info pages and kmalloc large > allocations, which are currently the only users of alloc_kmem_pages, but > it gets extremely inconvenient if one wants to make use of batched free > (e.g. to charge page tables - see release_pages) or page reference > counter (pipe buffers - see anon_pipe_buf_release). > > To overcome this limitation, this patch moves kmemcg uncharge code to > the generic free path and zaps free_kmem_pages helper. To distinguish > kmem pages from other page types, it makes alloc_kmem_pages initialize > page->_mapcount to a special value and introduces a new PageKmem helper, > which returns true if it sees this value. As far as I can tell, this new use of page._mapcount is OK, but... - The documentation for _mapcount needs to be updated (mm_types.h) - Don't believe the documentation! Because someone else may have done what you tried to do. Please manually audit mm/ for _mapcount uses. - One such use is "For recording whether a page is in the buddy system, we set ->_mapcount PAGE_BUDDY_MAPCOUNT_VALUE". Please update the comment for this while you're in there. (Including description of the state's lifetime). - And please update _mapcount docs for PageBalloon() - Why is the code accessing ->_mapcount directly? afaict page_mapcount() and friends will work OK? - The patch adds overhead to all kernels, even non-kmemcg and non-memcg kernels. Bad. Fixable? - PAGE_BUDDY_MAPCOUNT_VALUE, PAGE_BALLOON_MAPCOUNT_VALUE and PAGE_KMEM_MAPCOUNT_VALUE should all be put next to each other so readers can see all the possible values and so we don't get duplicates, etc. -- 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>