Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> writes: > On Mon, 10 Dec 2012 10:39:13 +0900 > Atsushi Kumagai <kumagai-atsushi@xxxxxxxxxxxxxxxxx> wrote: > >> This patch adds the values related to buddy system to vmcoreinfo data >> so that makedumpfile (dump filtering command) can filter out all free >> pages with the new logic. >> It's faster than the current logic because it can distinguish free page >> by analyzing page structure at the same time as filtering for other >> unnecessary pages (e.g. anonymous page). >> OTOH, the current logic has to trace free_list to distinguish free >> pages while analyzing page structure to filter out other unnecessary >> pages. >> >> The new logic uses the fact that buddy page is marked by _mapcount == >> PAGE_BUDDY_MAPCOUNT_VALUE. But, _mapcount shares its memory with other >> fields for SLAB/SLUB when PG_slab is set, so we need to check if PG_slab >> is set or not before looking up _mapcount value. >> And we can get the order of buddy system from private field. >> To sum it up, the values below are required for this logic. >> >> Required values: >> - OFFSET(page._mapcount) >> - OFFSET(page.private) >> - NUMBER(PG_slab) >> - NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE) >> >> Changelog from v1 to v2: >> 1. remove SIZE(pageflags) >> The new logic was changed after I sent v1 patch. >> Accordingly, SIZE(pageflags) has been unnecessary for makedumpfile. >> >> What's makedumpfile: >> makedumpfile creates a small dumpfile by excluding unnecessary pages >> for the analysis. To distinguish unnecessary pages, makedumpfile gets >> the vmcoreinfo data which has the minimum debugging information only >> for dump filtering. > > Gee, this info is getting highly dependent upon deep internal kernel > behaviour. > >> index 5e4bd78..b27efe4 100644 >> --- a/kernel/kexec.c >> +++ b/kernel/kexec.c >> @@ -1490,6 +1490,8 @@ static int __init crash_save_vmcoreinfo_init(void) >> VMCOREINFO_OFFSET(page, _count); >> VMCOREINFO_OFFSET(page, mapping); >> VMCOREINFO_OFFSET(page, lru); >> + VMCOREINFO_OFFSET(page, _mapcount); >> + VMCOREINFO_OFFSET(page, private); >> VMCOREINFO_OFFSET(pglist_data, node_zones); >> VMCOREINFO_OFFSET(pglist_data, nr_zones); >> #ifdef CONFIG_FLAT_NODE_MEM_MAP >> @@ -1512,6 +1514,8 @@ static int __init crash_save_vmcoreinfo_init(void) >> VMCOREINFO_NUMBER(PG_lru); >> VMCOREINFO_NUMBER(PG_private); >> VMCOREINFO_NUMBER(PG_swapcache); >> + VMCOREINFO_NUMBER(PG_slab); >> + VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE); > > We might change the PageBuddy() implementation at any time, and > makedumpfile will break. Or in this case, become less efficient. > > Is there any way in which we can move some of this logic into the > kernel? In this case, add some kernel code which uses PageBuddy() on > behalf of makedumpfile, rather than replicating the PageBuddy() logic > in userspace? All that exists when makedumpfile runs is a core file. So it would have to be something like a share library that builds with the kernel and then makedumpfile loads. Eric -- 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>