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From: Yajun Deng In-Reply-To: <20230929090406.GV3303@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: F24564001C X-Rspam-User: X-Stat-Signature: xxh4zecm67j5q1zafqrmhuf6zhifbtwj X-Rspamd-Server: rspam01 X-HE-Tag: 1695982257-228142 X-HE-Meta: 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 JJSJrhuk AIr/xjGifbk8Ep0X+5KSyCNtITCNagBEY8RJ8aqunJ8zHFYrhuSpGZ0odMgDwVuMgwXAATxvPTIT2vSYBOV5H+IhVq32RYLP8b+9JMb7UwTiYuTi22yiQH8IkPkIFq9h1V0s7tT8IIXp1Hb0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2023/9/29 17:04, Mike Rapoport wrote: > On Thu, Sep 28, 2023 at 04:47:59PM +0800, Yajun Deng wrote: >> On 2023/9/28 14:16, Mike Rapoport wrote: >>> 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. >> >> Yes, it has no obvious actual effect on the boot time,  but it does reduce >> the number of unnecessary loop. >> >> The actual effect on the boot time should not be the only criterion for >> whether a patch is accepted or not. >> >> Since the comment in the previous code, it tells the user that it would be >> executed twice, this can be misleading to users. >> >> So the new code will be simpler and clearer. It not just change the code, >> but also remove the comment > Adding return-by-pointer parameters to memblock_double_array() and pulling > memblock_reserve() out of this function is in no way simpler and clearer > that having an extra loop. If memblock_reserve() in memblock_double_array(),  there will be nested calls to memblock_add_range(). memblock_add_range(A)->memblock_double_array(A)->memblock_reserve(B)->memblock_add_range(B) ->memblock_insert_region(B)->memblock_merge_regions(B)->memblock_insert_region(A)->memblock_merge_regions(A) It's hard to see that and debug. If memblock_reserve() out of memblock_double_array(),  there wouldn't have a nested calls. memblock_add_range(A)->memblock_double_array(A)->memblock_insert_region(A)->memblock_merge_regions(A)-> memblock_reserve(B)->memblock_add_range(B)->memblock_insert_region(B)->memblock_merge_regions(B) We should make memblock_add_range is done, and do another memblock_add_range. > If the comment is wrong, just fix the comment. > >> about "executed twice",  it obviously tells the user only resize the array >> if it is equal to the maximum value >> >> and doesn't need to be executed twice. >> >>>> Signed-off-by: Yajun Deng >>>> --- >>>> 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 >>>>