On Wed, 2013-09-04 at 10:05 +0800, Tang Chen wrote: > On 09/04/2013 08:37 AM, Toshi Kani wrote: > > On Tue, 2013-08-27 at 17:37 +0800, Tang Chen wrote: > >> memblock_alloc_base_nid() is a common API of memblock. And it calls > >> memblock_find_in_range_node() with %start = 0, which means it has no > >> limit for the lowest address by default. > >> > >> memblock_find_in_range_node(0, max_addr, size, align, nid); > >> > >> Since we introduced current_limit_low to memblock, if we have no limit > >> for the lowest address or we are not sure, we should pass > >> MEMBLOCK_ALLOC_ACCESSIBLE to %start so that it will be limited by the > >> default low limit. > >> > >> dma_contiguous_reserve() and setup_log_buf() will eventually call > >> memblock_alloc_base_nid() to allocate memory. So if the allocation order > >> is from low to high, they will allocate memory from the lowest limit > >> to higher memory. > > > > This requires the callers to use MEMBLOCK_ALLOC_ACCESSIBLE instead of 0. > > Is there a good way to make sure that all callers will follow this rule > > going forward? Perhaps, memblock_find_in_range_node() should emit some > > message if 0 is passed when current_order is low to high and the boot > > option is specified? > > How about set this as the default rule: > > When using from low to high order, always allocate memory from > current_limit_low. > > So far, I think only movablenode boot option will use this order. Sounds good to me. > > Similarly, I wonder if we should have a check to the allocation size to > > make sure that all allocations will stay small in this case. > > > > We can check the size. But what is the stragety after we found that the > size > is too large ? Do we refuse to allocate memory ? I don't think so. We can just add a log message. No need to fail. > I think only relocate_initrd() and reserve_crachkernel() could allocate > large > memory. reserve_crachkernel() is easy to reorder, but reordering > relocate_initrd() > is difficult because acpi_initrd_override() need to access to it with va. > > I think on most servers, we don't need to do relocate_initrd(). initrd > will be > loaded to mapped memory in normal situation. Can we just leave it there ? Since this approach relies on the assumption that all allocations are small enough, it would be nice to have a way to verify if it remains true. How about we measure a total amount of allocations while the order is low to high, and log it when switched to high to low? This way, we can easily monitor the usage. Thanks, -Toshi -- 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>