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Date: Mon, 29 Mar 2021 18:13:04 -0700
From: Roman Gushchin <guro@...com>
To: Mike Kravetz <mike.kravetz@...cle.com>
CC: <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
Michal Hocko <mhocko@...e.com>,
Shakeel Butt <shakeelb@...gle.com>,
Oscar Salvador <osalvador@...e.de>,
David Hildenbrand <david@...hat.com>,
Muchun Song <songmuchun@...edance.com>,
David Rientjes <rientjes@...gle.com>,
Miaohe Lin <linmiaohe@...wei.com>,
Peter Zijlstra <peterz@...radead.org>,
Matthew Wilcox <willy@...radead.org>,
HORIGUCHI NAOYA <naoya.horiguchi@....com>,
"Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
Waiman Long <longman@...hat.com>, Peter Xu <peterx@...hat.com>,
Mina Almasry <almasrymina@...gle.com>,
Hillf Danton <hdanton@...a.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Barry Song <song.bao.hua@...ilicon.com>,
Will Deacon <will@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 1/8] mm/cma: change cma mutex to irq safe spinlock
On Mon, Mar 29, 2021 at 04:23:55PM -0700, Mike Kravetz wrote:
> Ideally, cma_release could be called from any context. However, that is
> not possible because a mutex is used to protect the per-area bitmap.
> Change the bitmap to an irq safe spinlock.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
Acked-by: Roman Gushchin <guro@...com>
Thanks!
> ---
> mm/cma.c | 20 +++++++++++---------
> mm/cma.h | 2 +-
> mm/cma_debug.c | 10 ++++++----
> 3 files changed, 18 insertions(+), 14 deletions(-)
>
> diff --git a/mm/cma.c b/mm/cma.c
> index b2393b892d3b..80875fd4487b 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -24,7 +24,6 @@
> #include <linux/memblock.h>
> #include <linux/err.h>
> #include <linux/mm.h>
> -#include <linux/mutex.h>
> #include <linux/sizes.h>
> #include <linux/slab.h>
> #include <linux/log2.h>
> @@ -83,13 +82,14 @@ static void cma_clear_bitmap(struct cma *cma, unsigned long pfn,
> unsigned int count)
> {
> unsigned long bitmap_no, bitmap_count;
> + unsigned long flags;
>
> bitmap_no = (pfn - cma->base_pfn) >> cma->order_per_bit;
> bitmap_count = cma_bitmap_pages_to_bits(cma, count);
>
> - mutex_lock(&cma->lock);
> + spin_lock_irqsave(&cma->lock, flags);
> bitmap_clear(cma->bitmap, bitmap_no, bitmap_count);
> - mutex_unlock(&cma->lock);
> + spin_unlock_irqrestore(&cma->lock, flags);
> }
>
> static void __init cma_activate_area(struct cma *cma)
> @@ -118,7 +118,7 @@ static void __init cma_activate_area(struct cma *cma)
> pfn += pageblock_nr_pages)
> init_cma_reserved_pageblock(pfn_to_page(pfn));
>
> - mutex_init(&cma->lock);
> + spin_lock_init(&cma->lock);
>
> #ifdef CONFIG_CMA_DEBUGFS
> INIT_HLIST_HEAD(&cma->mem_head);
> @@ -391,8 +391,9 @@ static void cma_debug_show_areas(struct cma *cma)
> unsigned long start = 0;
> unsigned long nr_part, nr_total = 0;
> unsigned long nbits = cma_bitmap_maxno(cma);
> + unsigned long flags;
>
> - mutex_lock(&cma->lock);
> + spin_lock_irqsave(&cma->lock, flags);
> pr_info("number of available pages: ");
> for (;;) {
> next_zero_bit = find_next_zero_bit(cma->bitmap, nbits, start);
> @@ -407,7 +408,7 @@ static void cma_debug_show_areas(struct cma *cma)
> start = next_zero_bit + nr_zero;
> }
> pr_cont("=> %lu free of %lu total pages\n", nr_total, cma->count);
> - mutex_unlock(&cma->lock);
> + spin_unlock_irqrestore(&cma->lock, flags);
> }
> #else
> static inline void cma_debug_show_areas(struct cma *cma) { }
> @@ -430,6 +431,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
> unsigned long pfn = -1;
> unsigned long start = 0;
> unsigned long bitmap_maxno, bitmap_no, bitmap_count;
> + unsigned long flags;
> size_t i;
> struct page *page = NULL;
> int ret = -ENOMEM;
> @@ -454,12 +456,12 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
> goto out;
>
> for (;;) {
> - mutex_lock(&cma->lock);
> + spin_lock_irqsave(&cma->lock, flags);
> bitmap_no = bitmap_find_next_zero_area_off(cma->bitmap,
> bitmap_maxno, start, bitmap_count, mask,
> offset);
> if (bitmap_no >= bitmap_maxno) {
> - mutex_unlock(&cma->lock);
> + spin_unlock_irqrestore(&cma->lock, flags);
> break;
> }
> bitmap_set(cma->bitmap, bitmap_no, bitmap_count);
> @@ -468,7 +470,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
> * our exclusive use. If the migration fails we will take the
> * lock again and unmark it.
> */
> - mutex_unlock(&cma->lock);
> + spin_unlock_irqrestore(&cma->lock, flags);
>
> pfn = cma->base_pfn + (bitmap_no << cma->order_per_bit);
> ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA,
> diff --git a/mm/cma.h b/mm/cma.h
> index 68ffad4e430d..2c775877eae2 100644
> --- a/mm/cma.h
> +++ b/mm/cma.h
> @@ -15,7 +15,7 @@ struct cma {
> unsigned long count;
> unsigned long *bitmap;
> unsigned int order_per_bit; /* Order of pages represented by one bit */
> - struct mutex lock;
> + spinlock_t lock;
> #ifdef CONFIG_CMA_DEBUGFS
> struct hlist_head mem_head;
> spinlock_t mem_head_lock;
> diff --git a/mm/cma_debug.c b/mm/cma_debug.c
> index d5bf8aa34fdc..6379cfbfd568 100644
> --- a/mm/cma_debug.c
> +++ b/mm/cma_debug.c
> @@ -35,11 +35,12 @@ static int cma_used_get(void *data, u64 *val)
> {
> struct cma *cma = data;
> unsigned long used;
> + unsigned long flags;
>
> - mutex_lock(&cma->lock);
> + spin_lock_irqsave(&cma->lock, flags);
> /* pages counter is smaller than sizeof(int) */
> used = bitmap_weight(cma->bitmap, (int)cma_bitmap_maxno(cma));
> - mutex_unlock(&cma->lock);
> + spin_unlock_irqrestore(&cma->lock, flags);
> *val = (u64)used << cma->order_per_bit;
>
> return 0;
> @@ -52,8 +53,9 @@ static int cma_maxchunk_get(void *data, u64 *val)
> unsigned long maxchunk = 0;
> unsigned long start, end = 0;
> unsigned long bitmap_maxno = cma_bitmap_maxno(cma);
> + unsigned long flags;
>
> - mutex_lock(&cma->lock);
> + spin_lock_irqsave(&cma->lock, flags);
> for (;;) {
> start = find_next_zero_bit(cma->bitmap, bitmap_maxno, end);
> if (start >= bitmap_maxno)
> @@ -61,7 +63,7 @@ static int cma_maxchunk_get(void *data, u64 *val)
> end = find_next_bit(cma->bitmap, bitmap_maxno, start);
> maxchunk = max(end - start, maxchunk);
> }
> - mutex_unlock(&cma->lock);
> + spin_unlock_irqrestore(&cma->lock, flags);
> *val = (u64)maxchunk << cma->order_per_bit;
>
> return 0;
> --
> 2.30.2
>
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