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    SubjectRe: [PATCH v3 2/5] mm: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn()
    On Sun, Mar 25, 2018 at 08:02:16PM -0700, Jia He wrote:
    >Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
    >where possible") optimized the loop in memmap_init_zone(). But there is
    >still some room for improvement. E.g. if pfn and pfn+1 are in the same
    >memblock region, we can simply pfn++ instead of doing the binary search
    >in memblock_next_valid_pfn. This patch only works when
    >CONFIG_HAVE_ARCH_PFN_VALID is enable.
    >
    >Signed-off-by: Jia He <jia.he@hxt-semitech.com>
    >---
    > include/linux/memblock.h | 2 +-
    > mm/memblock.c | 73 +++++++++++++++++++++++++++++-------------------
    > mm/page_alloc.c | 3 +-
    > 3 files changed, 47 insertions(+), 31 deletions(-)
    >
    >diff --git a/include/linux/memblock.h b/include/linux/memblock.h
    >index efbbe4b..a8fb2ab 100644
    >--- a/include/linux/memblock.h
    >+++ b/include/linux/memblock.h
    >@@ -204,7 +204,7 @@ void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
    > #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
    >
    > #ifdef CONFIG_HAVE_ARCH_PFN_VALID
    >-unsigned long memblock_next_valid_pfn(unsigned long pfn);
    >+unsigned long memblock_next_valid_pfn(unsigned long pfn, int *idx);
    > #endif
    >
    > /**
    >diff --git a/mm/memblock.c b/mm/memblock.c
    >index bea5a9c..06c1a08 100644
    >--- a/mm/memblock.c
    >+++ b/mm/memblock.c
    >@@ -1102,35 +1102,6 @@ void __init_memblock __next_mem_pfn_range(int *idx, int nid,
    > *out_nid = r->nid;
    > }
    >
    >-#ifdef CONFIG_HAVE_ARCH_PFN_VALID
    >-unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn)
    >-{
    >- struct memblock_type *type = &memblock.memory;
    >- unsigned int right = type->cnt;
    >- unsigned int mid, left = 0;
    >- phys_addr_t addr = PFN_PHYS(++pfn);
    >-
    >- do {
    >- mid = (right + left) / 2;
    >-
    >- if (addr < type->regions[mid].base)
    >- right = mid;
    >- else if (addr >= (type->regions[mid].base +
    >- type->regions[mid].size))
    >- left = mid + 1;
    >- else {
    >- /* addr is within the region, so pfn is valid */
    >- return pfn;
    >- }
    >- } while (left < right);
    >-
    >- if (right == type->cnt)
    >- return -1UL;
    >- else
    >- return PHYS_PFN(type->regions[right].base);
    >-}
    >-#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
    >-
    > /**
    > * memblock_set_node - set node ID on memblock regions
    > * @base: base of area to set node ID for
    >@@ -1162,6 +1133,50 @@ int __init_memblock memblock_set_node(phys_addr_t base, phys_addr_t size,
    > }
    > #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
    >
    >+#ifdef CONFIG_HAVE_ARCH_PFN_VALID
    >+unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn,
    >+ int *last_idx)
    >+{
    >+ struct memblock_type *type = &memblock.memory;
    >+ unsigned int right = type->cnt;
    >+ unsigned int mid, left = 0;
    >+ unsigned long start_pfn, end_pfn;
    >+ phys_addr_t addr = PFN_PHYS(++pfn);
    >+
    >+ /* fast path, return pfh+1 if next pfn is in the same region */
    ^^^ pfn

    >+ if (*last_idx != -1) {
    >+ start_pfn = PFN_DOWN(type->regions[*last_idx].base);

    To me, it should be PFN_UP().

    >+ end_pfn = PFN_DOWN(type->regions[*last_idx].base +
    >+ type->regions[*last_idx].size);
    >+
    >+ if (pfn < end_pfn && pfn > start_pfn)

    Could be (pfn < end_pfn && pfn >= start_pfn)?

    pfn == start_pfn is also a valid address.

    >+ return pfn;
    >+ }
    >+
    >+ /* slow path, do the binary searching */
    >+ do {
    >+ mid = (right + left) / 2;
    >+
    >+ if (addr < type->regions[mid].base)
    >+ right = mid;
    >+ else if (addr >= (type->regions[mid].base +
    >+ type->regions[mid].size))
    >+ left = mid + 1;
    >+ else {
    >+ *last_idx = mid;
    >+ return pfn;
    >+ }
    >+ } while (left < right);
    >+
    >+ if (right == type->cnt)
    >+ return -1UL;
    >+
    >+ *last_idx = right;
    >+
    >+ return PHYS_PFN(type->regions[*last_idx].base);
    >+}
    >+#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/

    The same comment as Daniel, you are moving the function out of
    CONFIG_HAVE_MEMBLOCK_NODE_MAP.

    >+
    > static phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
    > phys_addr_t align, phys_addr_t start,
    > phys_addr_t end, int nid, ulong flags)
    >diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    >index 2a967f7..0bb0274 100644
    >--- a/mm/page_alloc.c
    >+++ b/mm/page_alloc.c
    >@@ -5459,6 +5459,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
    > unsigned long end_pfn = start_pfn + size;
    > pg_data_t *pgdat = NODE_DATA(nid);
    > unsigned long pfn;
    >+ int idx = -1;
    > unsigned long nr_initialised = 0;
    > struct page *page;
    > #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
    >@@ -5490,7 +5491,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
    > * end_pfn), such that we hit a valid pfn (or end_pfn)
    > * on our next iteration of the loop.
    > */
    >- pfn = memblock_next_valid_pfn(pfn) - 1;
    >+ pfn = memblock_next_valid_pfn(pfn, &idx) - 1;
    > #endif
    > continue;
    > }
    >--
    >2.7.4

    --
    Wei Yang
    Help you, Help me

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