Commit 046169f0 authored by Yufen Yu's avatar Yufen Yu Committed by Song Liu
Browse files

md/raid5: let multiple devices of stripe_head share page 



In current implementation, grow_buffers() uses alloc_page() to
allocate the buffers for each stripe_head, i.e. allocate a page
for each dev[i] in stripe_head.

After setting stripe_size as a configurable value by writing
sysfs entry, it means that we always allocate 64K buffers, but
just use 4K of them when stripe_size is 4K in 64KB arm64.

To avoid wasting memory, we try to let multiple sh->dev share
one real page. That means, multiple sh->dev[i].page will point
to the only page with different offset. Example of 64K PAGE_SIZE
and 4K stripe_size as following:

                    64K PAGE_SIZE
          +---+---+---+---+------------------------------+
          |   |   |   |   |
          |   |   |   |   |
          +-+-+-+-+-+-+-+-+------------------------------+
            ^   ^   ^   ^
            |   |   |   +----------------------------+
            |   |   |                                |
            |   |   +-------------------+            |
            |   |                       |            |
            |   +----------+            |            |
            |              |            |            |
            +-+            |            |            |
              |            |            |            |
        +-----+-----+------+-----+------+-----+------+------+
sh      | offset(0) | offset(4K) | offset(8K) | offset(12K) |
 +      +-----------+------------+------------+-------------+
 +----> dev[0].page  dev[1].page  dev[2].page  dev[3].page

A new 'pages' array will be added into stripe_head to record shared
page used by this stripe_head. Allocate them when grow_buffers()
and free them when shrink_buffers().

After trying to share page, the users of sh->dev[i].page need to take
care of the related page offset: page of issued bio and page passed
to xor compution functions. But thanks for previous different page offset
supported. Here, we just need to set correct dev[i].offset.

Signed-off-by: default avatarYufen Yu <yuyufen@huawei.com>
Signed-off-by: default avatarSong Liu <songliubraving@fb.com>
parent 4f86ff55

drivers/md/raid5.c

+87 −2
Original line number Diff line number Diff line
@@ -448,13 +448,74 @@ out: 
	return sh;

}



static void shrink_buffers(struct stripe_head *sh)

#if PAGE_SIZE != DEFAULT_STRIPE_SIZE

static void free_stripe_pages(struct stripe_head *sh)

{

	int i;

	struct page *p;



	/* Have not allocate page pool */

	if (!sh->pages)

		return;



	for (i = 0; i < sh->nr_pages; i++) {

		p = sh->pages[i];

		if (p)

			put_page(p);

		sh->pages[i] = NULL;

	}

}



static int alloc_stripe_pages(struct stripe_head *sh, gfp_t gfp)

{

	int i;

	struct page *p;



	for (i = 0; i < sh->nr_pages; i++) {

		/* The page have allocated. */

		if (sh->pages[i])

			continue;



		p = alloc_page(gfp);

		if (!p) {

			free_stripe_pages(sh);

			return -ENOMEM;

		}

		sh->pages[i] = p;

	}

	return 0;

}



static int

init_stripe_shared_pages(struct stripe_head *sh, struct r5conf *conf, int disks)

{

	int nr_pages, cnt;



	if (sh->pages)

		return 0;



	/* Each of the sh->dev[i] need one conf->stripe_size */

	cnt = PAGE_SIZE / conf->stripe_size;

	nr_pages = (disks + cnt - 1) / cnt;



	sh->pages = kcalloc(nr_pages, sizeof(struct page *), GFP_KERNEL);

	if (!sh->pages)

		return -ENOMEM;

	sh->nr_pages = nr_pages;

	sh->stripes_per_page = cnt;

	return 0;

}

#endif



static void shrink_buffers(struct stripe_head *sh)

{

	int i;

	int num = sh->raid_conf->pool_size;



#if PAGE_SIZE == DEFAULT_STRIPE_SIZE

	for (i = 0; i < num ; i++) {

		struct page *p;



		WARN_ON(sh->dev[i].page != sh->dev[i].orig_page);

		p = sh->dev[i].page;

		if (!p)
@@ -462,6 +523,11 @@ static void shrink_buffers(struct stripe_head *sh) 
		sh->dev[i].page = NULL;

		put_page(p);

	}

#else

	for (i = 0; i < num; i++)

		sh->dev[i].page = NULL;

	free_stripe_pages(sh); /* Free pages */

#endif

}



static int grow_buffers(struct stripe_head *sh, gfp_t gfp)
@@ -469,6 +535,7 @@ static int grow_buffers(struct stripe_head *sh, gfp_t gfp) 
	int i;

	int num = sh->raid_conf->pool_size;



#if PAGE_SIZE == DEFAULT_STRIPE_SIZE

	for (i = 0; i < num; i++) {

		struct page *page;
@@ -479,7 +546,16 @@ static int grow_buffers(struct stripe_head *sh, gfp_t gfp) 
		sh->dev[i].orig_page = page;

		sh->dev[i].offset = 0;

	}

#else

	if (alloc_stripe_pages(sh, gfp))

		return -ENOMEM;



	for (i = 0; i < num; i++) {

		sh->dev[i].page = raid5_get_dev_page(sh, i);

		sh->dev[i].orig_page = sh->dev[i].page;

		sh->dev[i].offset = raid5_get_page_offset(sh, i);

	}

#endif

	return 0;

}
@@ -2205,6 +2281,9 @@ static void raid_run_ops(struct stripe_head *sh, unsigned long ops_request) 


static void free_stripe(struct kmem_cache *sc, struct stripe_head *sh)

{

#if PAGE_SIZE != DEFAULT_STRIPE_SIZE

	kfree(sh->pages);

#endif

	if (sh->ppl_page)

		__free_page(sh->ppl_page);

	kmem_cache_free(sc, sh);
@@ -2238,9 +2317,15 @@ static struct stripe_head *alloc_stripe(struct kmem_cache *sc, gfp_t gfp, 
			sh->ppl_page = alloc_page(gfp);

			if (!sh->ppl_page) {

				free_stripe(sc, sh);

				sh = NULL;

				return NULL;

			}

		}

#if PAGE_SIZE != DEFAULT_STRIPE_SIZE

		if (init_stripe_shared_pages(sh, conf, disks)) {

			free_stripe(sc, sh);

			return NULL;

		}

#endif

	}

	return sh;

}

drivers/md/raid5.h

+27 −1
Original line number Diff line number Diff line
@@ -195,6 +195,7 @@ enum reconstruct_states { 
	reconstruct_state_result,

};



#define DEFAULT_STRIPE_SIZE	4096

struct stripe_head {

	struct hlist_node	hash;

	struct list_head	lru;	      /* inactive_list or handle_list */
@@ -246,6 +247,13 @@ struct stripe_head { 
		int 		     target, target2;

		enum sum_check_flags zero_sum_result;

	} ops;



#if PAGE_SIZE != DEFAULT_STRIPE_SIZE

	/* These pages will be used by bios in dev[i] */

	struct page	**pages;

	int	nr_pages;	/* page array size */

	int	stripes_per_page;

#endif

	struct r5dev {

		/* rreq and rvec are used for the replacement device when

		 * writing data to both devices.
@@ -473,7 +481,6 @@ struct disk_info { 
 */



#define NR_STRIPES		256

#define DEFAULT_STRIPE_SIZE	4096



#if PAGE_SIZE == DEFAULT_STRIPE_SIZE

#define STRIPE_SIZE		PAGE_SIZE
@@ -772,6 +779,25 @@ static inline int algorithm_is_DDF(int layout) 
	return layout >= 8 && layout <= 10;

}



#if PAGE_SIZE != DEFAULT_STRIPE_SIZE

/*

 * Return offset of the corresponding page for r5dev.

 */

static inline int raid5_get_page_offset(struct stripe_head *sh, int disk_idx)

{

	return (disk_idx % sh->stripes_per_page) * RAID5_STRIPE_SIZE(sh->raid_conf);

}



/*

 * Return corresponding page address for r5dev.

 */

static inline struct page *

raid5_get_dev_page(struct stripe_head *sh, int disk_idx)

{

	return sh->pages[disk_idx / sh->stripes_per_page];

}

#endif



extern void md_raid5_kick_device(struct r5conf *conf);

extern int raid5_set_cache_size(struct mddev *mddev, int size);

extern sector_t raid5_compute_blocknr(struct stripe_head *sh, int i, int previous);

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