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Message-ID: <20230928061619.GS3303@kernel.org>
Date: Thu, 28 Sep 2023 09:16:19 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Yajun Deng <yajun.deng@...ux.dev>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memblock: don't run loop in memblock_add_range() twice
On Wed, Sep 27, 2023 at 09:37:52AM +0800, Yajun Deng wrote:
> There is round twice in memblock_add_range(). The first counts the number
> of regions needed to accommodate the new area. The second actually inserts
> them. But the first round isn't really needed, we just need to check the
> counts before inserting them.
>
> Check the count before calling memblock_insert_region(). If the count is
> equal to the maximum value, it needs to resize the array. Otherwise,
> insert it directly.
>
> To avoid nested calls to memblock_add_range(), we need to call
> memblock_reserve() out of memblock_double_array().
memblock_add_range() does an extra loop once in a while, but I don't think
removing it will have any actual effect on the boot time.
> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> ---
> mm/memblock.c | 117 ++++++++++++++++++++++++--------------------------
> 1 file changed, 57 insertions(+), 60 deletions(-)
>
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 5a88d6d24d79..3f44c84f5d0b 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -400,6 +400,8 @@ void __init memblock_discard(void)
> * @type: memblock type of the regions array being doubled
> * @new_area_start: starting address of memory range to avoid overlap with
> * @new_area_size: size of memory range to avoid overlap with
> + * @new_reserve_base: starting address of new array
> + * @new_reserve_size: size of new array
> *
> * Double the size of the @type regions array. If memblock is being used to
> * allocate memory for a new reserved regions array and there is a previously
> @@ -412,7 +414,9 @@ void __init memblock_discard(void)
> */
> static int __init_memblock memblock_double_array(struct memblock_type *type,
> phys_addr_t new_area_start,
> - phys_addr_t new_area_size)
> + phys_addr_t new_area_size,
> + phys_addr_t *new_reserve_base,
> + phys_addr_t *new_reserve_size)
> {
> struct memblock_region *new_array, *old_array;
> phys_addr_t old_alloc_size, new_alloc_size;
> @@ -490,11 +494,13 @@ static int __init_memblock memblock_double_array(struct memblock_type *type,
> memblock_free(old_array, old_alloc_size);
>
> /*
> - * Reserve the new array if that comes from the memblock. Otherwise, we
> - * needn't do it
> + * Keep the address and size if that comes from the memblock. Otherwise,
> + * we needn't do it.
> */
> - if (!use_slab)
> - BUG_ON(memblock_reserve(addr, new_alloc_size));
> + if (!use_slab) {
> + *new_reserve_base = addr;
> + *new_reserve_size = new_alloc_size;
> + }
>
> /* Update slab flag */
> *in_slab = use_slab;
> @@ -588,11 +594,12 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
> phys_addr_t base, phys_addr_t size,
> int nid, enum memblock_flags flags)
> {
> - bool insert = false;
> phys_addr_t obase = base;
> phys_addr_t end = base + memblock_cap_size(base, &size);
> - int idx, nr_new, start_rgn = -1, end_rgn;
> + phys_addr_t new_base = 0, new_size;
> + int idx, start_rgn = -1, end_rgn;
> struct memblock_region *rgn;
> + unsigned long ocnt = type->cnt;
>
> if (!size)
> return 0;
> @@ -608,25 +615,6 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
> return 0;
> }
>
> - /*
> - * The worst case is when new range overlaps all existing regions,
> - * then we'll need type->cnt + 1 empty regions in @type. So if
> - * type->cnt * 2 + 1 is less than or equal to type->max, we know
> - * that there is enough empty regions in @type, and we can insert
> - * regions directly.
> - */
> - if (type->cnt * 2 + 1 <= type->max)
> - insert = true;
> -
> -repeat:
> - /*
> - * The following is executed twice. Once with %false @insert and
> - * then with %true. The first counts the number of regions needed
> - * to accommodate the new area. The second actually inserts them.
> - */
> - base = obase;
> - nr_new = 0;
> -
> for_each_memblock_type(idx, type, rgn) {
> phys_addr_t rbase = rgn->base;
> phys_addr_t rend = rbase + rgn->size;
> @@ -644,15 +632,23 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
> WARN_ON(nid != memblock_get_region_node(rgn));
> #endif
> WARN_ON(flags != rgn->flags);
> - nr_new++;
> - if (insert) {
> - if (start_rgn == -1)
> - start_rgn = idx;
> - end_rgn = idx + 1;
> - memblock_insert_region(type, idx++, base,
> - rbase - base, nid,
> - flags);
> - }
> +
> + /*
> + * If type->cnt is equal to type->max, it means there's
> + * not enough empty region and the array needs to be
> + * resized. Otherwise, insert it directly.
> + */
> + if ((type->cnt == type->max) &&
> + memblock_double_array(type, obase, size,
> + &new_base, &new_size))
> + return -ENOMEM;
> +
> + if (start_rgn == -1)
> + start_rgn = idx;
> + end_rgn = idx + 1;
> + memblock_insert_region(type, idx++, base,
> + rbase - base, nid,
> + flags);
> }
> /* area below @rend is dealt with, forget about it */
> base = min(rend, end);
> @@ -660,33 +656,28 @@ static int __init_memblock memblock_add_range(struct memblock_type *type,
>
> /* insert the remaining portion */
> if (base < end) {
> - nr_new++;
> - if (insert) {
> - if (start_rgn == -1)
> - start_rgn = idx;
> - end_rgn = idx + 1;
> - memblock_insert_region(type, idx, base, end - base,
> - nid, flags);
> - }
> + if ((type->cnt == type->max) &&
> + memblock_double_array(type, obase, size,
> + &new_base, &new_size))
> + return -ENOMEM;
> +
> + if (start_rgn == -1)
> + start_rgn = idx;
> + end_rgn = idx + 1;
> + memblock_insert_region(type, idx, base, end - base,
> + nid, flags);
> }
>
> - if (!nr_new)
> + if (ocnt == type->cnt)
> return 0;
>
> - /*
> - * If this was the first round, resize array and repeat for actual
> - * insertions; otherwise, merge and return.
> - */
> - if (!insert) {
> - while (type->cnt + nr_new > type->max)
> - if (memblock_double_array(type, obase, size) < 0)
> - return -ENOMEM;
> - insert = true;
> - goto repeat;
> - } else {
> - memblock_merge_regions(type, start_rgn, end_rgn);
> - return 0;
> - }
> + memblock_merge_regions(type, start_rgn, end_rgn);
> +
> + /* Reserve the new array */
> + if (new_base)
> + memblock_reserve(new_base, new_size);
> +
> + return 0;
> }
>
> /**
> @@ -755,6 +746,7 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
> int *start_rgn, int *end_rgn)
> {
> phys_addr_t end = base + memblock_cap_size(base, &size);
> + phys_addr_t new_base = 0, new_size;
> int idx;
> struct memblock_region *rgn;
>
> @@ -764,10 +756,15 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
> return 0;
>
> /* we'll create at most two more regions */
> - while (type->cnt + 2 > type->max)
> - if (memblock_double_array(type, base, size) < 0)
> + if (type->cnt + 2 > type->max) {
> + if (memblock_double_array(type, base, size,
> + &new_base, &new_size))
> return -ENOMEM;
>
> + if (new_base)
> + memblock_reserve(new_base, new_size);
> + }
> +
> for_each_memblock_type(idx, type, rgn) {
> phys_addr_t rbase = rgn->base;
> phys_addr_t rend = rbase + rgn->size;
> --
> 2.25.1
>
--
Sincerely yours,
Mike.
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