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SubjectRe: [patch 4/4] mm: bootmem: try harder to free pages in bulk
On Tue, Dec 13, 2011 at 02:58:31PM +0100, Johannes Weiner wrote:
> The loop that frees pages to the page allocator while bootstrapping
> tries to free higher-order blocks only when the starting address is
> aligned to that block size. Otherwise it will free all pages on that
> node one-by-one.
>
> Change it to free individual pages up to the first aligned block and
> then try higher-order frees from there.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
I gave all four patches a try now on my ARM machine and it still works
fine. But note that this patch isn't really tested, because for me
free_all_bootmem_core is only called once and that with an aligned
address.
But at least you didn't broke that case :-)
Having said that, I wonder if the code does the right thing for
unaligned start. (That is, it's wrong to start testing for bit 0 of
map[idx / BITS_PER_LONG], isn't it?) But if that's the case that's not
something you introduced in this series.

One more comment below.

> ---
> mm/bootmem.c | 22 ++++++++++------------
> 1 files changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/mm/bootmem.c b/mm/bootmem.c
> index 1aea171..668e94d 100644
> --- a/mm/bootmem.c
> +++ b/mm/bootmem.c
> @@ -171,7 +171,6 @@ void __init free_bootmem_late(unsigned long addr, unsigned long size)
>
> static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
> {
> - int aligned;
> struct page *page;
> unsigned long start, end, pages, count = 0;
>
> @@ -181,14 +180,8 @@ static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
> start = bdata->node_min_pfn;
> end = bdata->node_low_pfn;
>
> - /*
> - * If the start is aligned to the machines wordsize, we might
> - * be able to free pages in bulks of that order.
> - */
> - aligned = !(start & (BITS_PER_LONG - 1));
> -
> - bdebug("nid=%td start=%lx end=%lx aligned=%d\n",
> - bdata - bootmem_node_data, start, end, aligned);
> + bdebug("nid=%td start=%lx end=%lx\n",
> + bdata - bootmem_node_data, start, end);
>
> while (start < end) {
> unsigned long *map, idx, vec;
> @@ -196,12 +189,17 @@ static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
> map = bdata->node_bootmem_map;
> idx = start - bdata->node_min_pfn;
> vec = ~map[idx / BITS_PER_LONG];
> -
> - if (aligned && vec == ~0UL) {
> + /*
> + * If we have a properly aligned and fully unreserved
> + * BITS_PER_LONG block of pages in front of us, free
> + * it in one go.
> + */
> + if (IS_ALIGNED(start, BITS_PER_LONG) && vec == ~0UL) {
> int order = ilog2(BITS_PER_LONG);
>
> __free_pages_bootmem(pfn_to_page(start), order);
> count += BITS_PER_LONG;
> + start += BITS_PER_LONG;
> } else {
> unsigned long off = 0;
>
> @@ -214,8 +212,8 @@ static unsigned long __init free_all_bootmem_core(bootmem_data_t *bdata)
> vec >>= 1;
> off++;
> }
> + start = ALIGN(start + 1, BITS_PER_LONG);
> }
> - start += BITS_PER_LONG;
I don't know if the compiler would be more happy if you would just use

start = ALIGN(start + 1, BITS_PER_LONG);

unconditionally and drop

start += BITS_PER_LONG

in the if block?!

Best regards
Uwe

--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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