On Wed, Oct 04, 2023 at 12:30:45AM +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 memblock_insert_region. If the count is equal to > the maximum, it needs to resize the array. Otherwise, insert it directly. > > Also, there is a nested call here, we need to reserve the current array > immediately if slab is unavailable. I presume this fixes a bug you found in v2, but are you sure it'll _never_ explode on a machine with different memory layout and different sequence of memblock_reservee() calls? I don't see this micro-optimization is worth the churn and potential bugs. NAK. > Signed-off-by: Yajun Deng <yajun.deng@xxxxxxxxx> > --- > v3: reserve the current array immediately if slab is unavailable. > v2: remove the changes of memblock_double_array. > v1: https://lore.kernel.org/all/20230927013752.2515238-1-yajun.deng@xxxxxxxxx/ > --- > mm/memblock.c | 93 +++++++++++++++++++++++---------------------------- > 1 file changed, 41 insertions(+), 52 deletions(-) > > diff --git a/mm/memblock.c b/mm/memblock.c > index 5a88d6d24d79..71449c0b8bc8 100644 > --- a/mm/memblock.c > +++ b/mm/memblock.c > @@ -588,11 +588,12 @@ 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; > + int idx, start_rgn = -1, end_rgn; > struct memblock_region *rgn; > + int use_slab = slab_is_available(); > + unsigned long ocnt = type->cnt; > > if (!size) > return 0; > @@ -608,25 +609,6 @@ 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 +626,30 @@ 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 slab is unavailable, it means a new array was reserved > + * in memblock_double_array. There is a nested call here, We > + * need to reserve the current array now if its type is > + * reserved. > + */ > + if (type->cnt == type->max) { > + if (memblock_double_array(type, obase, size)) > + return -ENOMEM; > + else if (!use_slab && type == &memblock.reserved) > + return memblock_reserve(obase, size); > } > + > + 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 +657,25 @@ 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) { > + if (memblock_double_array(type, obase, size)) > + return -ENOMEM; > + else if (!use_slab && type == &memblock.reserved) > + return memblock_reserve(obase, size); > } > - } > > - if (!nr_new) > - return 0; > + if (start_rgn == -1) > + start_rgn = idx; > + end_rgn = idx + 1; > + memblock_insert_region(type, idx, base, end - base, > + nid, flags); > + } > > - /* > - * 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 { > + if (ocnt != type->cnt) > memblock_merge_regions(type, start_rgn, end_rgn); > - return 0; > - } > + > + return 0; > } > > /** > -- > 2.25.1 > -- Sincerely yours, Mike.
