From: Petr Tesarik <ptesarik@xxxxxxx>
Subject: [PATCH v2 2/3] Generic handling of multi-page exclusions
Date: Fri, 4 Apr 2014 19:25:08 +0200
> When multiple pages are excluded from the dump, store the extents in the
> mem_map_data structure, and check if anything is still pending on the
> next invocation of __exclude_unnecessary_pages for the same mem_map.
>
> The start PFN of the excluded extent is set to the end of the current
> cycle (which is equal to the start of the next cycle, see update_cycle),
> so only the part of the excluded region which falls beyond current cycle
> buffer is valid. If the excluded region is completely processed in the
> current cycle, the start PFN is even bigger than the end PFN. That
> causes nothing to be done at the beginning of the next cycle.
>
> There is no check whether the adjusted pfn_start is still within the
> current cycle. Nothing bad happens if it isn't, because exclude_range()
> is used again to exclude the remaining part, so even if the excluded
> region happens to span more than two cycles, the code will still work
> correctly.
>
> Note that clear_bit_on_2nd_bitmap_for_kernel() accepts PFNs outside the
> current cyclic range. It willreturn FALSE, so such PFNs are not counted.
>
> Signed-off-by: Petr Tesarik <ptesarik at suse.cz>
> ---
> makedumpfile.c | 47 +++++++++++++++++++++++++++++++++--------------
> makedumpfile.h | 7 +++++++
> 2 files changed, 40 insertions(+), 14 deletions(-)
>
> diff --git a/makedumpfile.c b/makedumpfile.c
> index 81c687b..9ffb901 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -2385,6 +2385,9 @@ dump_mem_map(unsigned long long pfn_start,
> mmd->pfn_end = pfn_end;
> mmd->mem_map = mem_map;
>
> + mmd->exclude_pfn_start = 0ULL;
> + mmd->exclude_pfn_end = 0ULL;
> +
> DEBUG_MSG("mem_map (%d)\n", num_mm);
> DEBUG_MSG(" mem_map : %lx\n", mem_map);
> DEBUG_MSG(" pfn_start : %llx\n", pfn_start);
> @@ -4657,6 +4660,21 @@ initialize_2nd_bitmap_cyclic(struct cycle *cycle)
> return TRUE;
> }
>
> +static void
> +exclude_range(unsigned long long *counter, struct mem_map_data *mmd,
> + unsigned long long pfn, unsigned long long endpfn, struct cycle *cycle)
> +{
> + while (pfn < endpfn) {
> + if (clear_bit_on_2nd_bitmap_for_kernel(pfn, cycle))
> + (*counter)++;
> + ++pfn;
> + }
Here endpfn is pfn + nr_pages in __exclude_unnecessary_pages(), and
the pfn could be cycle->end_pfn <= pfn < endpfn.
while (pfn < MIN(endpfn, cycle->end_pfn) {
if (clear_bit_on_2nd_bitmap_for_kernel(pfn, cycle))
(*counter)++;
++pfn;
}
> +
> + mmd->exclude_pfn_start = cycle ? cycle->end_pfn : ULONGLONG_MAX;
When does cycle become NULL?
Along with the above point,
mmd->exclude_pfn_start = MIN(endpfn, cycle->end_pfn);
and then we can continue the processing in the next cycle.
> + mmd->exclude_pfn_end = endpfn;
> + mmd->exclude_pfn_counter = counter;
> +}
> +
> int
> __exclude_unnecessary_pages(struct mem_map_data *mmd, struct cycle *cycle)
> {
> @@ -4671,6 +4689,18 @@ __exclude_unnecessary_pages(struct mem_map_data *mmd, struct cycle *cycle)
> unsigned long flags, mapping, private = 0;
>
> /*
> + * If a multi-page exclusion is pending, do it first
> + */
> + if (mmd->exclude_pfn_start < mmd->exclude_pfn_end) {
> + exclude_range(mmd->exclude_pfn_counter, mmd,
> + mmd->exclude_pfn_start, mmd->exclude_pfn_end,
> + cycle);
> +
> + mem_map += (mmd->exclude_pfn_end - pfn_start) * SIZE(page);
> + pfn_start = mmd->exclude_pfn_end;
> + }
> +
> + /*
> * Refresh the buffer of struct page, when changing mem_map.
> */
> pfn_read_start = ULONGLONG_MAX;
> @@ -4734,21 +4764,10 @@ __exclude_unnecessary_pages(struct mem_map_data *mmd, struct cycle *cycle)
> if ((info->dump_level & DL_EXCLUDE_FREE)
> && info->page_is_buddy
> && info->page_is_buddy(flags, _mapcount, private, _count)) {
> - int i, nr_pages = 1 << private;
> + int nr_pages = 1 << private;
> +
> + exclude_range(&pfn_free, mmd, pfn, pfn + nr_pages, cycle);
>
> - for (i = 0; i < nr_pages; ++i) {
> - /*
> - * According to combination of
> - * MAX_ORDER and size of cyclic
> - * buffer, this clearing bit operation
> - * can overrun the cyclic buffer.
> - *
> - * See check_cyclic_buffer_overrun()
> - * for the detail.
> - */
> - if (clear_bit_on_2nd_bitmap_for_kernel((pfn + i), cycle))
> - pfn_free++;
> - }
> pfn += nr_pages - 1;
> mem_map += (nr_pages - 1) * SIZE(page);
> }
> diff --git a/makedumpfile.h b/makedumpfile.h
> index 951ed1b..dfad569 100644
> --- a/makedumpfile.h
> +++ b/makedumpfile.h
> @@ -816,6 +816,13 @@ struct mem_map_data {
> unsigned long long pfn_start;
> unsigned long long pfn_end;
> unsigned long mem_map;
> +
> + /*
> + * for excluding multi-page regions
> + */
> + unsigned long exclude_pfn_start;
> + unsigned long exclude_pfn_end;
unsigned long long exclude_pfn_start;
unsigned long long exclude_pfn_end;
The integers representing page frame numbers need to be defined as
unsigned long long for architectures where physical address can have
64-bit length but unsigned long has 32-bit only, such as x86 PAE.
Kumagai-san, I saw this sometimes in the past. How about introducing
specific abstract type for page frame number like below?
typedef unsigned long long pfn_t;
maybe with some prefix. I think this also helps code readability
because unsigned long long is too long.
> + unsigned long long *exclude_pfn_counter;
> };
Also, it seems to me better to introduce a new type for this
processing rather than extending existing code. struct mem_map_data is
not specific for the excluding processing.
Thanks.
HATAYAMA, Daisuke
