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Introducing defer free > mechanism to buffer some which make the allocation easier. The shrinker will > ensure the page block can be reclaimed when there is memory pressure. > > Signed-off-by: Zhaoyang Huang > --- > v2: fix build warning and regist shrinker > --- > --- > mm/cma.c | 151 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- > mm/cma.h | 11 +++++ > 2 files changed, 160 insertions(+), 2 deletions(-) > > diff --git a/mm/cma.c b/mm/cma.c > index 4a978e0..6d2fd24 100644 > --- a/mm/cma.c > +++ b/mm/cma.c > @@ -39,6 +39,10 @@ > unsigned cma_area_count; > static DEFINE_MUTEX(cma_mutex); > > +static unsigned long cma_defer_free_count(struct shrinker *shrinker, > + struct shrink_control *sc); > +static unsigned long cma_defer_free_scan(struct shrinker *shrinker, > + struct shrink_control *sc); > phys_addr_t cma_get_base(const struct cma *cma) > { > return PFN_PHYS(cma->base_pfn); > @@ -153,6 +157,20 @@ static int __init cma_init_reserved_areas(void) > } > core_initcall(cma_init_reserved_areas); > > +static unsigned long cma_free_get(struct cma *cma) > +{ > + unsigned long used; > + unsigned long val; > + > + spin_lock_irq(&cma->lock); > + /* pages counter is smaller than sizeof(int) */ > + used = bitmap_weight(cma->bitmap, (int)cma_bitmap_maxno(cma)); > + val = cma->count - ((u64)used << cma->order_per_bit); > + spin_unlock_irq(&cma->lock); > + > + return val; > +} > + > void __init cma_reserve_pages_on_error(struct cma *cma) > { > cma->reserve_pages_on_error = true; > @@ -212,6 +230,13 @@ int __init cma_init_reserved_mem(phys_addr_t base, phys_addr_t size, > cma_area_count++; > totalcma_pages += (size / PAGE_SIZE); > > + cma->batch = cma->count >> 1; > + cma->shrinker.count_objects = cma_defer_free_count; > + cma->shrinker.scan_objects = cma_defer_free_scan; > + cma->shrinker.seeks = DEFAULT_SEEKS; > + cma->shrinker.batch = 0; > + > + register_shrinker(&cma->shrinker, "cma-shrinker"); > return 0; > } > > @@ -411,6 +436,46 @@ static void cma_debug_show_areas(struct cma *cma) > static inline void cma_debug_show_areas(struct cma *cma) { } > #endif > > +static int cma_defer_area_fetch(struct cma *cma, unsigned long pfn, > + unsigned long count) > +{ > + struct cma_defer_free_area *area; > + unsigned long new_pfn; > + int ret = -1; > + > + if (!atomic64_read(&cma->defer_count)) > + return ret; > + if (count <= atomic64_read(&cma->defer_count)) { > + spin_lock_irq(&cma->lock); > + list_for_each_entry(area, &cma->defer_free, list) { > + /*area found for given pfn and count*/ > + if (pfn >= area->pfn && count <= area->count) { > + list_del(&area->list); > + /*set bits for allocated pfn*/ > + bitmap_set(cma->bitmap, pfn - cma->base_pfn, count); > + kfree(area); > + atomic64_sub(count, &cma->defer_count); > + /*release the rest pfn to cma*/ > + if (!list_empty(&cma->defer_free) && (pfn == area->pfn)) { There is a null pointer reference here？