On Tue, Jul 13, 2010 at 12:53:48AM +0900, Minchan Kim wrote: > Kukjin, Could you test below patch? > I don't have any sparsemem system. Sorry. > > -- CUT DOWN HERE -- > > Kukjin reported oops happen while he change min_free_kbytes > http://www.spinics.net/lists/arm-kernel/msg92894.html > It happen by memory map on sparsemem. > > The system has a memory map following as. > section 0 section 1 section 2 > 0x20000000-0x25000000, 0x40000000-0x50000000, 0x50000000-0x58000000 > SECTION_SIZE_BITS 28(256M) > > It means section 0 is an incompletely filled section. > Nontheless, current pfn_valid of sparsemem checks pfn loosely. > > It checks only mem_section's validation. > So in above case, pfn on 0x25000000 can pass pfn_valid's validation check. > It's not what we want. > > The Following patch adds check valid pfn range check on pfn_valid of sparsemem. Look at the declaration of struct mem_section for a second. It is meant to partition address space uniformly into backed and unbacked areas. It comes with implicit size and offset information by means of SECTION_SIZE_BITS and the section's index in the section array. Now you are not okay with the _granularity_ but propose to change _the model_ by introducing a subsection within each section and at the same time make the concept of a section completely meaningless: its size becomes arbitrary and its associated mem_map and flags will apply to the subsection only. My question is: if the sections are not fine-grained enough, why not just make them? The biggest possible section size to describe the memory population on this machine accurately is 16M. Why not set SECTION_SIZE_BITS to 24? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>