On 12/05/2017 12:22 PM, Vlastimil Babka wrote: > On 12/04/2017 01:56 PM, zhong jiang wrote: >> On 2017/12/4 20:35, Michal Hocko wrote: >>> On Mon 04-12-17 20:23:49, zhong jiang wrote: >>>> On 2017/12/4 20:01, Michal Hocko wrote: >>>>> On Mon 04-12-17 19:51:12, zhong jiang wrote: >>>>>> On 2017/12/2 1:15, Michal Hocko wrote: >>>>>>> On Fri 01-12-17 17:58:28, Vlastimil Babka wrote: >>>>>>>> On 11/30/2017 11:15 PM, akpm@xxxxxxxxxxxxxxxxxxxx wrote: >>>>>>>>> From: zhong jiang <zhongjiang@xxxxxxxxxx> >>>>>>>>> Subject: mm/page_owner: align with pageblock_nr pages >>>>>>>>> >>>>>>>>> When pfn_valid(pfn) returns false, pfn should be aligned with >>>>>>>>> pageblock_nr_pages other than MAX_ORDER_NR_PAGES in init_pages_in_zone, >>>>>>>>> because the skipped 2M may be valid pfn, as a result, early allocated >>>>>>>>> count will not be accurate. >>>>>>>>> >>>>>>>>> Link: http://lkml.kernel.org/r/1468938136-24228-1-git-send-email-zhongjiang@xxxxxxxxxx >>>>>>>>> Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx> >>>>>>>>> Cc: Michal Hocko <mhocko@xxxxxxxxxx> >>>>>>>>> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> >>>>>>>> The author never responded and Michal Hocko basically NAKed it in >>>>>>>> https://lkml.kernel.org/r/<20160812130727.GI3639@xxxxxxxxxxxxxx> >>>>>>>> I think we should drop it. >>>>>>> Or extend the changelog to actually describe what kind of problem it >>>>>>> fixes and do an additional step to unigy >>>>>>> MAX_ORDER_NR_PAGES/pageblock_nr_pages >>>>>>> >>>>>> Hi, Michal >>>>>> >>>>>> IIRC, I had explained the reason for patch. if it not. I am so sorry for that. >>>>>> >>>>>> when we select MAX_ORDER_NR_PAGES, the second 2M will be skiped. >>>>>> it maybe result in normal pages leak. >>>>>> >>>>>> meanwhile. as you had said. it make the code consistent. why do not we do it. >>>>>> >>>>>> I think it is reasonable to upstream the patch. maybe I should rewrite the changelog >>>>>> and repost it. >>>>>> >>>>>> Michal, Do you think ? >>>>> Yes, rewrite the patch changelog and make it _clear_ what it fixes and >>>>> under _what_ conditions. There are also other places using >>>>> MAX_ORDER_NR_PAGES rathern than pageblock_nr_pages. Do they need to be >>>>> updated as well? >>>> in the lastest kernel. according to correspond context, I can not find the candidate. :-) >>> git grep says some in page_ext.c, memory_hotplug.c and few in the arch >>> code. I belive we really want to describe and document the distinction >>> between the two constants and explain when to use which one. >>> >> yes, limited by my knowledge and english. Maybe Vlastimil can address it in detail. > > Hi, on a fresh look, I believe this patch doesn't improve anything in > practice. It potentially makes init_pages_in_zone() catch more early > allocations, if a hole happens to be placed in the beginning of > MAX_ORDER block, and the following pageblock within the block was early > allocated. > > However, read_page_owner() skips whole MAX_ORDER block as well in this > situation, so we won't be able to read the info anyway... > > Also the problem is not as simple as documenting MAX_ORDER_NR_PAGES vs > pabeblock_nr_pages. We discussed it year ago when this patch was first > posted, how skipping over holes would have to be made more robust, and > how architectures should define hole granularity to avoid checking each > individual pfn in what appears to be a hole, to see if the hole has ended. OK, let's see. There are three archs that define CONFIG_HOLES_IN_ZONE. This means for those arches, pfn_valid_within() is not defined as true, but calls actual pfn_valid(): arm64 - pfn_valid(pfn) is memblock_is_map_memory(pfn << PAGE_SHIFT) What is the granularity of memblock allocator? If it's less than MAX_ORDER, could we just sacrifice the memory in MAX_ORDER block that has a hole inside? mips - pfn_valid() is a simple pfn-within-boundaries comparison. That shouldn't make any difference, if we observe zone end pfn right! They added the config in 465aaed0030b2 for Cavium Octeon and apparently it fixed a crash, but I wonder what was really going on then... ia64 - uses ia64_pfn_valid() which I have no idea what it does... > >> Thanks >> zhongjiang >> > > -- > 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> > -- 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>
