On 2012-8-21 11:55, Petr Tesarik wrote: > Dne Po 20. srpna 2012 08:38:10 wujianguo napsal(a): >> From: Jianguo Wu <wujianguo@xxxxxxxxxx> >> >> Hi all, >> I think zone->present_pages indicates pages that buddy system can >> management, it should be: >> zone->present_pages = spanned pages - absent pages - bootmem pages, >> but now: >> zone->present_pages = spanned pages - absent pages - memmap pages. >> spanned pages：total size, including holes. >> absent pages: holes. >> bootmem pages: pages used in system boot, managed by bootmem allocator. >> memmap pages: pages used by page structs. > > Absolutely. The memory allocated to page structs should be counted in. > Hi Petr, Bootmem pages include the memory allocated to page structs. Thanks! Jianguo Wu >> This may cause zone->present_pages less than it should be. >> For example, numa node 1 has ZONE_NORMAL and ZONE_MOVABLE, >> it's memmap and other bootmem will be allocated from ZONE_MOVABLE, >> so ZONE_NORMAL's present_pages should be spanned pages - absent pages, >> but now it also minus memmap pages(free_area_init_core), which are actually >> allocated from ZONE_MOVABLE. When offline all memory of a zone, This will >> cause zone->present_pages less than 0, because present_pages is unsigned >> long type, it is actually a very large integer, it indirectly caused >> zone->watermark[WMARK_MIN] become a large >> integer(setup_per_zone_wmarks()), than cause totalreserve_pages become a >> large integer(calculate_totalreserve_pages()), and finally cause memory >> allocating failure when fork process(__vm_enough_memory()). >> >> [root@localhost ~]# dmesg >> -bash: fork: Cannot allocate memory >> >> I think bug described in http://marc.info/?l=linux-mm&m=134502182714186&w=2 >> is also caused by wrong zone present pages. > > And yes, I can confirm that the bug I reported is caused by a too low number > for the present pages counter. Your patch does fix the bug for me. > > Thanks! > Petr Tesarik > -- 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>