[1/6] block: manage bio slab cache by xarray

Commit Message

Ming Lei Dec. 30, 2020, 12:32 a.m. UTC

Managing bio slab cache via xarray by using slab cache size as xarray index, and
storing 'struct bio_slab' instance into xarray.

So code is simplified a lot, meantime is is more readable than before.

Signed-off-by: Ming Lei <[e-mail]>
---
 block/bio.c | 104 +++++++++++++++++++++-------------------------------
 1 file changed, 42 insertions(+), 62 deletions(-)

Comments

Christoph Hellwig Jan. 4, 2021, 8:54 a.m. UTC | #1

On Wed, Dec 30, 2020 at 08:32:50AM +0800, Ming Lei wrote:
> Managing bio slab cache via xarray by using slab cache size as xarray index, and

Overly long line in the commit log above.

> +static struct bio_slab *create_bio_slab(unsigned int size)
> +{
> +	struct bio_slab *bslab = kzalloc(sizeof(*bslab), GFP_KERNEL);
> +	if (!bslab)
> +		return NULL;

Missing whitespace after the variable declaration.

> +
> +	snprintf(bslab->name, sizeof(bslab->name), "bio-%d", size);
> +	bslab->slab = kmem_cache_create(bslab->name, size,
> +			ARCH_KMALLOC_MINALIGN, SLAB_HWCACHE_ALIGN, NULL);
> +	if (bslab->slab) {
> +		bslab->slab_ref = 1;
> +		bslab->slab_size = size;
> +	} else {
> +		kfree(bslab);
> +		bslab = NULL;
> +	}
> +	return bslab;
> +}

I'd simply this to:

	if (!bslab->slab) {
		kfree(bslab);
		return NULL;
	}

	bslab->slab_ref = 1;
	bslab->slab_size = size;
	return bslab;
}

>  
>  static struct kmem_cache *bio_find_or_create_slab(unsigned int extra_size)
>  {
>  	unsigned int sz = sizeof(struct bio) + extra_size;
>  	struct kmem_cache *slab = NULL;
> +	struct bio_slab *bslab;
>  
>  	mutex_lock(&bio_slab_lock);
> +	bslab = xa_load(&bio_slabs, sz);
> +	if (bslab) {
> +		slab = bslab->slab;
> +		bslab->slab_ref++;
> +	} else {
> +		bslab = create_bio_slab(sz);
> +		if(bslab && !xa_err(xa_store(&bio_slabs, sz, bslab,
> +						GFP_KERNEL)))

Missing whitespace after the "if"

But more importantly, I'd expect the xa_store to go into create_bio_slab
to make the code a little more readable and to consolidate the error
handling.  Also we really shouldn't need the slab local variable in
this function.

>  static void bio_put_slab(struct bio_set *bs)
>  {
>  	struct bio_slab *bslab = NULL;
> +	unsigned int slab_size = bs->front_pad + sizeof(struct bio) +
> +		BIO_INLINE_VECS * sizeof(struct bio_vec);

This calculation would look nice factored out into a little helper with
a comment explaining it.

Patch

diff --git a/block/bio.c b/block/bio.c
index 1f2cc1fbe283..aa657cdd7c8c 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -19,6 +19,7 @@ 
 #include <linux/highmem.h>
 #include <linux/sched/sysctl.h>
 #include <linux/blk-crypto.h>
+#include <linux/xarray.h>
 
 #include <trace/events/block.h>
 #include "blk.h"
@@ -58,61 +59,49 @@  struct bio_slab {
 	char name[8];
 };
 static DEFINE_MUTEX(bio_slab_lock);
-static struct bio_slab *bio_slabs;
-static unsigned int bio_slab_nr, bio_slab_max;
+static DEFINE_XARRAY(bio_slabs);
+
+static struct bio_slab *create_bio_slab(unsigned int size)
+{
+	struct bio_slab *bslab = kzalloc(sizeof(*bslab), GFP_KERNEL);
+	if (!bslab)
+		return NULL;
+
+	snprintf(bslab->name, sizeof(bslab->name), "bio-%d", size);
+	bslab->slab = kmem_cache_create(bslab->name, size,
+			ARCH_KMALLOC_MINALIGN, SLAB_HWCACHE_ALIGN, NULL);
+	if (bslab->slab) {
+		bslab->slab_ref = 1;
+		bslab->slab_size = size;
+	} else {
+		kfree(bslab);
+		bslab = NULL;
+	}
+	return bslab;
+}
 
 static struct kmem_cache *bio_find_or_create_slab(unsigned int extra_size)
 {
 	unsigned int sz = sizeof(struct bio) + extra_size;
 	struct kmem_cache *slab = NULL;
-	struct bio_slab *bslab, *new_bio_slabs;
-	unsigned int new_bio_slab_max;
-	unsigned int i, entry = -1;
+	struct bio_slab *bslab;
 
 	mutex_lock(&bio_slab_lock);
-
-	i = 0;
-	while (i < bio_slab_nr) {
-		bslab = &bio_slabs[i];
-
-		if (!bslab->slab && entry == -1)
-			entry = i;
-		else if (bslab->slab_size == sz) {
+	bslab = xa_load(&bio_slabs, sz);
+	if (bslab) {
+		slab = bslab->slab;
+		bslab->slab_ref++;
+	} else {
+		bslab = create_bio_slab(sz);
+		if(bslab && !xa_err(xa_store(&bio_slabs, sz, bslab,
+						GFP_KERNEL)))
 			slab = bslab->slab;
-			bslab->slab_ref++;
-			break;
+		else {
+			if (bslab)
+				kmem_cache_destroy(bslab->slab);
+			kfree(bslab);
 		}
-		i++;
-	}
-
-	if (slab)
-		goto out_unlock;
-
-	if (bio_slab_nr == bio_slab_max && entry == -1) {
-		new_bio_slab_max = bio_slab_max << 1;
-		new_bio_slabs = krealloc(bio_slabs,
-					 new_bio_slab_max * sizeof(struct bio_slab),
-					 GFP_KERNEL);
-		if (!new_bio_slabs)
-			goto out_unlock;
-		bio_slab_max = new_bio_slab_max;
-		bio_slabs = new_bio_slabs;
 	}
-	if (entry == -1)
-		entry = bio_slab_nr++;
-
-	bslab = &bio_slabs[entry];
-
-	snprintf(bslab->name, sizeof(bslab->name), "bio-%d", entry);
-	slab = kmem_cache_create(bslab->name, sz, ARCH_KMALLOC_MINALIGN,
-				 SLAB_HWCACHE_ALIGN, NULL);
-	if (!slab)
-		goto out_unlock;
-
-	bslab->slab = slab;
-	bslab->slab_ref = 1;
-	bslab->slab_size = sz;
-out_unlock:
 	mutex_unlock(&bio_slab_lock);
 	return slab;
 }
@@ -120,27 +109,26 @@  static struct kmem_cache *bio_find_or_create_slab(unsigned int extra_size)
 static void bio_put_slab(struct bio_set *bs)
 {
 	struct bio_slab *bslab = NULL;
-	unsigned int i;
+	unsigned int slab_size = bs->front_pad + sizeof(struct bio) +
+		BIO_INLINE_VECS * sizeof(struct bio_vec);
 
 	mutex_lock(&bio_slab_lock);
 
-	for (i = 0; i < bio_slab_nr; i++) {
-		if (bs->bio_slab == bio_slabs[i].slab) {
-			bslab = &bio_slabs[i];
-			break;
-		}
-	}
-
+	bslab = xa_load(&bio_slabs, slab_size);
 	if (WARN(!bslab, KERN_ERR "bio: unable to find slab!\n"))
 		goto out;
 
+	WARN_ON_ONCE(bslab->slab != bs->bio_slab);
+
 	WARN_ON(!bslab->slab_ref);
 
 	if (--bslab->slab_ref)
 		goto out;
 
+	xa_erase(&bio_slabs, slab_size);
+
 	kmem_cache_destroy(bslab->slab);
-	bslab->slab = NULL;
+	kfree(bslab);
 
 out:
 	mutex_unlock(&bio_slab_lock);
@@ -1651,16 +1639,8 @@  static void __init biovec_init_slabs(void)
 
 static int __init init_bio(void)
 {
-	bio_slab_max = 2;
-	bio_slab_nr = 0;
-	bio_slabs = kcalloc(bio_slab_max, sizeof(struct bio_slab),
-			    GFP_KERNEL);
-
 	BUILD_BUG_ON(BIO_FLAG_LAST > BVEC_POOL_OFFSET);
 
-	if (!bio_slabs)
-		panic("bio: can't allocate bios\n");
-
 	bio_integrity_init();
 	biovec_init_slabs();