[PATCH 0/3] Fix zone revalidation memory allocation failures

[PATCH 0/3] Fix zone revalidation memory allocation failures

[Damien Le Moal]

This series addresses a reccuring problem with zone revalidation
failures observed during extensive testing with memory constrained
system and device hot-plugging.

The problem source is failure to allocate large memory areas with
alloc_pages() or kmalloc() in blk_revalidate_disk_zones() to store the
disk array of zones (struct blk_zone) or in sd_zbc_report_zones() for
the report zones command reply buffer.

The solution proposed here is to:
1) limit the number of zones to be reported with a single report zones
command execution, and
2) Use vmalloc to allocate large-ish arrays and buffers in place of
alloc_pages() and kmalloc().

With these changes, tests do not show any zone revalidation failures
while not impacting the time taken for a disk initial zone inspection
during device scan.

Damien Le Moal (3):
  block: Allow mapping of vmalloc-ed buffers
  sd_zbc: Fix report zones buffer allocation
  block: Limit zone array allocation size

 block/bio.c            |  8 ++++-
 block/blk-zoned.c      | 29 +++++++---------
 drivers/scsi/sd_zbc.c  | 79 +++++++++++++++++++++++++++++++-----------
 include/linux/blkdev.h |  5 +++
 4 files changed, 84 insertions(+), 37 deletions(-)

-- 
2.21.0

[PATCH 1/3] block: Allow mapping of vmalloc-ed buffers

[Damien Le Moal]

To allow the SCSI subsystem scsi_execute_req() function to issue
requests using large buffers that are better allocated with vmalloc()
rather than kmalloc(), modify bio_map_kern() to allow passing a buffer
allocated with the vmalloc() function. To do so, simply test the buffer
address using is_vmalloc_addr() and use vmalloc_to_page() instead of
virt_to_page() to obtain the pages of vmalloc-ed buffers.

Fixes: 515ce6061312 ("scsi: sd_zbc: Fix sd_zbc_report_zones() buffer allocation")
Fixes: e76239a3748c ("block: add a report_zones method")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
---
 block/bio.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index ce797d73bb43..05afcaf655f3 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1501,6 +1501,8 @@ struct bio *bio_map_kern(struct request_queue *q, void *data, unsigned int len,
 	unsigned long end = (kaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	unsigned long start = kaddr >> PAGE_SHIFT;
 	const int nr_pages = end - start;
+	bool is_vmalloc = is_vmalloc_addr(data);
+	struct page *page;
 	int offset, i;
 	struct bio *bio;
 
@@ -1518,7 +1520,11 @@ struct bio *bio_map_kern(struct request_queue *q, void *data, unsigned int len,
 		if (bytes > len)
 			bytes = len;
 
-		if (bio_add_pc_page(q, bio, virt_to_page(data), bytes,
+		if (is_vmalloc)
+			page = vmalloc_to_page(data);
+		else
+			page = virt_to_page(data);
+		if (bio_add_pc_page(q, bio, page, bytes,
 				    offset) < bytes) {
 			/* we don't support partial mappings */
 			bio_put(bio);
-- 
2.21.0

[PATCH 2/3] sd_zbc: Fix report zones buffer allocation

[Damien Le Moal]

During disk scan and revalidation done with sd_revalidate(), the zones
of a zoned disk are checked using the helper function
blk_revalidate_disk_zones() if a configuration change is detected
(change in the number of zones or zone size). The function
blk_revalidate_disk_zones() issues report_zones calls that are very
large, that is, to obtain zone information for all zones of the disk
with a single command. The size of the report zones command buffer
necessary for such large request generally is lower than the disk
max_hw_sectors and KMALLOC_MAX_SIZE (4MB) and succeeds on boot (no
memory fragmentation), but often fail at run time (e.g. hot-plug
event). This causes the disk revalidation to fail and the disk
capacity to be changed to 0.

This problem can be avoided by using vmalloc() instead of kmalloc() for
the buffer allocation. To limit the amount of memory to be allocated,
this patch also introduces the arbitrary SD_ZBC_REPORT_MAX_ZONES
maximum number of zones to report with a single report zones command.
This limit may be lowered further to satisfy the disk max_hw_sectors
limit. Finally, to ensure that the vmalloc-ed buffer can always be
mapped in a request, the buffer size is further limited to at most
queue_max_segments() pages, allowing successful mapping of the buffer
even in the worst case scenario where none of the buffer pages are
contiguous.

Fixes: 515ce6061312 ("scsi: sd_zbc: Fix sd_zbc_report_zones() buffer allocation")
Fixes: e76239a3748c ("block: add a report_zones method")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
---
 drivers/scsi/sd_zbc.c | 79 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 59 insertions(+), 20 deletions(-)

diff --git a/drivers/scsi/sd_zbc.c b/drivers/scsi/sd_zbc.c
index 7334024b64f1..b12444d6fc95 100644
--- a/drivers/scsi/sd_zbc.c
+++ b/drivers/scsi/sd_zbc.c
@@ -103,6 +103,48 @@ static int sd_zbc_do_report_zones(struct scsi_disk *sdkp, unsigned char *buf,
 	return 0;
 }
 
+/*
+ * Maximum number of zones to get with one report zones command.
+ */
+#define SD_ZBC_REPORT_MAX_ZONES		8192U
+
+/**
+ * Allocate a buffer for report zones reply.
+ * @disk: The target disk
+ * @nr_zones: Maximum number of zones to report
+ * @buflen: Size of the buffer allocated
+ * @gfp_mask: Memory allocation mask
+ *
+ */
+static void *sd_zbc_alloc_report_buffer(struct request_queue *q,
+					unsigned int nr_zones, size_t *buflen,
+					gfp_t gfp_mask)
+{
+	size_t bufsize;
+	void *buf;
+
+	/*
+	 * Report zone buffer size should be at most 64B times the number of
+	 * zones requested plus the 64B reply header, but should be at least
+	 * SECTOR_SIZE for ATA devices.
+	 * Make sure that this size does not exceed the hardware capabilities.
+	 * Furthermore, since the report zone command cannot be split, make
+	 * sure that the allocated buffer can always be mapped by limiting the
+	 * number of pages allocated to the HBA max segments limit.
+	 */
+	nr_zones = min(nr_zones, SD_ZBC_REPORT_MAX_ZONES);
+	bufsize = roundup((nr_zones + 1) * 64, 512);
+	bufsize = min_t(size_t, bufsize,
+			queue_max_hw_sectors(q) << SECTOR_SHIFT);
+	bufsize = min_t(size_t, bufsize, queue_max_segments(q) << PAGE_SHIFT);
+
+	buf = __vmalloc(bufsize, gfp_mask, PAGE_KERNEL);
+	if (buf)
+		*buflen = bufsize;
+
+	return buf;
+}
+
 /**
  * sd_zbc_report_zones - Disk report zones operation.
  * @disk: The target disk
@@ -118,9 +160,9 @@ int sd_zbc_report_zones(struct gendisk *disk, sector_t sector,
 			gfp_t gfp_mask)
 {
 	struct scsi_disk *sdkp = scsi_disk(disk);
-	unsigned int i, buflen, nrz = *nr_zones;
+	unsigned int i, nrz = *nr_zones;
 	unsigned char *buf;
-	size_t offset = 0;
+	size_t buflen = 0, offset = 0;
 	int ret = 0;
 
 	if (!sd_is_zoned(sdkp))
@@ -132,16 +174,14 @@ int sd_zbc_report_zones(struct gendisk *disk, sector_t sector,
 	 * without exceeding the device maximum command size. For ATA disks,
 	 * buffers must be aligned to 512B.
 	 */
-	buflen = min(queue_max_hw_sectors(disk->queue) << 9,
-		     roundup((nrz + 1) * 64, 512));
-	buf = kmalloc(buflen, gfp_mask);
+	buf = sd_zbc_alloc_report_buffer(disk->queue, nrz, &buflen, gfp_mask);
 	if (!buf)
 		return -ENOMEM;
 
 	ret = sd_zbc_do_report_zones(sdkp, buf, buflen,
 			sectors_to_logical(sdkp->device, sector), true);
 	if (ret)
-		goto out_free_buf;
+		goto out;
 
 	nrz = min(nrz, get_unaligned_be32(&buf[0]) / 64);
 	for (i = 0; i < nrz; i++) {
@@ -152,8 +192,8 @@ int sd_zbc_report_zones(struct gendisk *disk, sector_t sector,
 
 	*nr_zones = nrz;
 
-out_free_buf:
-	kfree(buf);
+out:
+	kvfree(buf);
 
 	return ret;
 }
@@ -287,8 +327,6 @@ static int sd_zbc_check_zoned_characteristics(struct scsi_disk *sdkp,
 	return 0;
 }
 
-#define SD_ZBC_BUF_SIZE 131072U
-
 /**
  * sd_zbc_check_zones - Check the device capacity and zone sizes
  * @sdkp: Target disk
@@ -304,22 +342,23 @@ static int sd_zbc_check_zoned_characteristics(struct scsi_disk *sdkp,
  */
 static int sd_zbc_check_zones(struct scsi_disk *sdkp, u32 *zblocks)
 {
+	size_t bufsize, buflen;
 	u64 zone_blocks = 0;
 	sector_t max_lba, block = 0;
 	unsigned char *buf;
 	unsigned char *rec;
-	unsigned int buf_len;
-	unsigned int list_length;
 	int ret;
 	u8 same;
 
 	/* Get a buffer */
-	buf = kmalloc(SD_ZBC_BUF_SIZE, GFP_KERNEL);
+	buf = sd_zbc_alloc_report_buffer(sdkp->disk->queue,
+					 SD_ZBC_REPORT_MAX_ZONES,
+					 &bufsize, GFP_NOIO);
 	if (!buf)
 		return -ENOMEM;
 
 	/* Do a report zone to get max_lba and the same field */
-	ret = sd_zbc_do_report_zones(sdkp, buf, SD_ZBC_BUF_SIZE, 0, false);
+	ret = sd_zbc_do_report_zones(sdkp, buf, bufsize, 0, false);
 	if (ret)
 		goto out_free;
 
@@ -355,12 +394,12 @@ static int sd_zbc_check_zones(struct scsi_disk *sdkp, u32 *zblocks)
 	do {
 
 		/* Parse REPORT ZONES header */
-		list_length = get_unaligned_be32(&buf[0]) + 64;
+		buflen = min_t(size_t, get_unaligned_be32(&buf[0]) + 64,
+			       bufsize);
 		rec = buf + 64;
-		buf_len = min(list_length, SD_ZBC_BUF_SIZE);
 
 		/* Parse zone descriptors */
-		while (rec < buf + buf_len) {
+		while (rec < buf + buflen) {
 			u64 this_zone_blocks = get_unaligned_be64(&rec[8]);
 
 			if (zone_blocks == 0) {
@@ -376,8 +415,8 @@ static int sd_zbc_check_zones(struct scsi_disk *sdkp, u32 *zblocks)
 		}
 
 		if (block < sdkp->capacity) {
-			ret = sd_zbc_do_report_zones(sdkp, buf, SD_ZBC_BUF_SIZE,
-						     block, true);
+			ret = sd_zbc_do_report_zones(sdkp, buf, bufsize, block,
+						     true);
 			if (ret)
 				goto out_free;
 		}
@@ -408,7 +447,7 @@ static int sd_zbc_check_zones(struct scsi_disk *sdkp, u32 *zblocks)
 	}
 
 out_free:
-	kfree(buf);
+	kvfree(buf);
 
 	return ret;
 }
-- 
2.21.0

[PATCH 3/3] block: Limit zone array allocation size

[Damien Le Moal]

Limit the size of the struct blk_zone array used in
blk_revalidate_disk_zones() to avoid memory allocation failures leading
to disk revalidation failure. Further reduce the likelyhood of these
failures by using kvmalloc() instead of directly allocating contiguous
pages.

Fixes: 515ce6061312 ("scsi: sd_zbc: Fix sd_zbc_report_zones() buffer allocation")
Fixes: e76239a3748c ("block: add a report_zones method")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
---
 block/blk-zoned.c      | 29 +++++++++++++----------------
 include/linux/blkdev.h |  5 +++++
 2 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index ae7e91bd0618..26f878b9b5f5 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -373,22 +373,20 @@ static inline unsigned long *blk_alloc_zone_bitmap(int node,
  * Allocate an array of struct blk_zone to get nr_zones zone information.
  * The allocated array may be smaller than nr_zones.
  */
-static struct blk_zone *blk_alloc_zones(int node, unsigned int *nr_zones)
+static struct blk_zone *blk_alloc_zones(unsigned int *nr_zones)
 {
-	size_t size = *nr_zones * sizeof(struct blk_zone);
-	struct page *page;
-	int order;
-
-	for (order = get_order(size); order >= 0; order--) {
-		page = alloc_pages_node(node, GFP_NOIO | __GFP_ZERO, order);
-		if (page) {
-			*nr_zones = min_t(unsigned int, *nr_zones,
-				(PAGE_SIZE << order) / sizeof(struct blk_zone));
-			return page_address(page);
-		}
+	struct blk_zone *zones;
+	size_t nrz = min(*nr_zones, BLK_ZONED_REPORT_MAX_ZONES);
+
+	zones = kvcalloc(nrz, sizeof(struct blk_zone), GFP_NOIO);
+	if (!zones) {
+		*nr_zones = 0;
+		return NULL;
 	}
 
-	return NULL;
+	*nr_zones = nrz;
+
+	return zones;
 }
 
 void blk_queue_free_zone_bitmaps(struct request_queue *q)
@@ -443,7 +441,7 @@ int blk_revalidate_disk_zones(struct gendisk *disk)
 
 	/* Get zone information and initialize seq_zones_bitmap */
 	rep_nr_zones = nr_zones;
-	zones = blk_alloc_zones(q->node, &rep_nr_zones);
+	zones = blk_alloc_zones(&rep_nr_zones);
 	if (!zones)
 		goto out;
 
@@ -480,8 +478,7 @@ int blk_revalidate_disk_zones(struct gendisk *disk)
 	blk_mq_unfreeze_queue(q);
 
 out:
-	free_pages((unsigned long)zones,
-		   get_order(rep_nr_zones * sizeof(struct blk_zone)));
+	kvfree(zones);
 	kfree(seq_zones_wlock);
 	kfree(seq_zones_bitmap);
 
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 592669bcc536..f7faac856017 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -344,6 +344,11 @@ struct queue_limits {
 
 #ifdef CONFIG_BLK_DEV_ZONED
 
+/*
+ * Maximum number of zones to report with a single report zones command.
+ */
+#define BLK_ZONED_REPORT_MAX_ZONES	8192U
+
 extern unsigned int blkdev_nr_zones(struct block_device *bdev);
 extern int blkdev_report_zones(struct block_device *bdev,
 			       sector_t sector, struct blk_zone *zones,
-- 
2.21.0

Re: [PATCH 1/3] block: Allow mapping of vmalloc-ed buffers

[Chaitanya Kulkarni]

Looks good with one nit, can be done at the time of applying patch.

Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>

On 6/24/19 7:46 PM, Damien Le Moal wrote:
> To allow the SCSI subsystem scsi_execute_req() function to issue
> requests using large buffers that are better allocated with vmalloc()
> rather than kmalloc(), modify bio_map_kern() to allow passing a buffer
> allocated with the vmalloc() function. To do so, simply test the buffer
> address using is_vmalloc_addr() and use vmalloc_to_page() instead of
> virt_to_page() to obtain the pages of vmalloc-ed buffers.
> 
> Fixes: 515ce6061312 ("scsi: sd_zbc: Fix sd_zbc_report_zones() buffer allocation")
> Fixes: e76239a3748c ("block: add a report_zones method")
> Cc: stable@vger.kernel.org
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> ---
>   block/bio.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index ce797d73bb43..05afcaf655f3 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1501,6 +1501,8 @@ struct bio *bio_map_kern(struct request_queue *q, void *data, unsigned int len,
>   	unsigned long end = (kaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
>   	unsigned long start = kaddr >> PAGE_SHIFT;
>   	const int nr_pages = end - start;
> +	bool is_vmalloc = is_vmalloc_addr(data); > +	struct page *page;
>   	int offset, i;
>   	struct bio *bio;
>   
> @@ -1518,7 +1520,11 @@ struct bio *bio_map_kern(struct request_queue *q, void *data, unsigned int len,
>   		if (bytes > len)
>   			bytes = len;
>   
> -		if (bio_add_pc_page(q, bio, virt_to_page(data), bytes,
> +		if (is_vmalloc)
nit:- Can we use is_vmalloc_addr() call directly so that
"if (is_vmalloc)" ->  "if (is_vmalloc_addr(data))" and remove is_vmalloc 
variable.
> +			page = vmalloc_to_page(data);
> +		else
> +			page = virt_to_page(data);
> +		if (bio_add_pc_page(q, bio, page, bytes,
>   				    offset) < bytes) {
>   			/* we don't support partial mappings */
>   			bio_put(bio);
> 

Re: [PATCH 2/3] sd_zbc: Fix report zones buffer allocation

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 3132 bytes --]

Hi Damien,

I love your patch! Yet something to improve:

[auto build test ERROR on block/for-next]
[also build test ERROR on v5.2-rc6 next-20190621]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Damien-Le-Moal/Fix-zone-revalidation-memory-allocation-failures/20190625-175053
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
config: sparc64-allyesconfig (attached as .config)
compiler: sparc64-linux-gcc (GCC) 7.4.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.4.0 make.cross ARCH=sparc64 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All error/warnings (new ones prefixed by >>):

   drivers/scsi/sd_zbc.c: In function 'sd_zbc_alloc_report_buffer':
>> drivers/scsi/sd_zbc.c:141:8: error: implicit declaration of function '__vmalloc'; did you mean '__kmalloc'? [-Werror=implicit-function-declaration]
     buf = __vmalloc(bufsize, gfp_mask, PAGE_KERNEL);
           ^~~~~~~~~
           __kmalloc
>> drivers/scsi/sd_zbc.c:141:6: warning: assignment makes pointer from integer without a cast [-Wint-conversion]
     buf = __vmalloc(bufsize, gfp_mask, PAGE_KERNEL);
         ^
   cc1: some warnings being treated as errors

vim +141 drivers/scsi/sd_zbc.c

   110	
   111	/**
   112	 * Allocate a buffer for report zones reply.
   113	 * @disk: The target disk
   114	 * @nr_zones: Maximum number of zones to report
   115	 * @buflen: Size of the buffer allocated
   116	 * @gfp_mask: Memory allocation mask
   117	 *
   118	 */
   119	static void *sd_zbc_alloc_report_buffer(struct request_queue *q,
   120						unsigned int nr_zones, size_t *buflen,
   121						gfp_t gfp_mask)
   122	{
   123		size_t bufsize;
   124		void *buf;
   125	
   126		/*
   127		 * Report zone buffer size should be at most 64B times the number of
   128		 * zones requested plus the 64B reply header, but should be at least
   129		 * SECTOR_SIZE for ATA devices.
   130		 * Make sure that this size does not exceed the hardware capabilities.
   131		 * Furthermore, since the report zone command cannot be split, make
   132		 * sure that the allocated buffer can always be mapped by limiting the
   133		 * number of pages allocated to the HBA max segments limit.
   134		 */
   135		nr_zones = min(nr_zones, SD_ZBC_REPORT_MAX_ZONES);
   136		bufsize = roundup((nr_zones + 1) * 64, 512);
   137		bufsize = min_t(size_t, bufsize,
   138				queue_max_hw_sectors(q) << SECTOR_SHIFT);
   139		bufsize = min_t(size_t, bufsize, queue_max_segments(q) << PAGE_SHIFT);
   140	
 > 141		buf = __vmalloc(bufsize, gfp_mask, PAGE_KERNEL);
   142		if (buf)
   143			*buflen = bufsize;
   144	
   145		return buf;
   146	}
   147	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 58537 bytes --]

Re: [PATCH 1/3] block: Allow mapping of vmalloc-ed buffers

[Bart Van Assche]

On 6/24/19 8:24 PM, Chaitanya Kulkarni wrote:
> nit:- Can we use is_vmalloc_addr() call directly so that
> "if (is_vmalloc)" ->  "if (is_vmalloc_addr(data))" and remove is_vmalloc
> variable.
That would change a single call of is_vmalloc_addr() into multiple?

Bart.

Re: [PATCH 1/3] block: Allow mapping of vmalloc-ed buffers

[Bart Van Assche]

On 6/24/19 7:46 PM, Damien Le Moal wrote:
> To allow the SCSI subsystem scsi_execute_req() function to issue
> requests using large buffers that are better allocated with vmalloc()
> rather than kmalloc(), modify bio_map_kern() to allow passing a buffer
> allocated with the vmalloc() function. To do so, simply test the buffer
> address using is_vmalloc_addr() and use vmalloc_to_page() instead of
> virt_to_page() to obtain the pages of vmalloc-ed buffers.
> 
> Fixes: 515ce6061312 ("scsi: sd_zbc: Fix sd_zbc_report_zones() buffer allocation")
> Fixes: e76239a3748c ("block: add a report_zones method")
> Cc: stable@vger.kernel.org
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> ---
>   block/bio.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index ce797d73bb43..05afcaf655f3 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1501,6 +1501,8 @@ struct bio *bio_map_kern(struct request_queue *q, void *data, unsigned int len,
>   	unsigned long end = (kaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
>   	unsigned long start = kaddr >> PAGE_SHIFT;
>   	const int nr_pages = end - start;
> +	bool is_vmalloc = is_vmalloc_addr(data);
> +	struct page *page;
>   	int offset, i;
>   	struct bio *bio;
>   
> @@ -1518,7 +1520,11 @@ struct bio *bio_map_kern(struct request_queue *q, void *data, unsigned int len,
>   		if (bytes > len)
>   			bytes = len;
>   
> -		if (bio_add_pc_page(q, bio, virt_to_page(data), bytes,
> +		if (is_vmalloc)
> +			page = vmalloc_to_page(data);
> +		else
> +			page = virt_to_page(data);
> +		if (bio_add_pc_page(q, bio, page, bytes,
>   				    offset) < bytes) {
>   			/* we don't support partial mappings */
>   			bio_put(bio);

Reviewed-by: Bart Van Assche <bvanassche@acm.org>

Re: [PATCH 1/3] block: Allow mapping of vmalloc-ed buffers

[Chaitanya Kulkarni]

On 06/25/2019 08:59 AM, Bart Van Assche wrote:
> On 6/24/19 8:24 PM, Chaitanya Kulkarni wrote:
>> nit:- Can we use is_vmalloc_addr() call directly so that
>> "if (is_vmalloc)" ->  "if (is_vmalloc_addr(data))" and remove is_vmalloc
>> variable.
> That would change a single call of is_vmalloc_addr() into multiple?

Well is_vmalloc_addr() it is an in-line helper with address comparison.

is it too expensive to have such a comparison in the loop ?

>
> Bart.
>

Re: [PATCH 2/3] sd_zbc: Fix report zones buffer allocation

[Bart Van Assche]

On 6/24/19 7:46 PM, Damien Le Moal wrote:
> During disk scan and revalidation done with sd_revalidate(), the zones
> of a zoned disk are checked using the helper function
> blk_revalidate_disk_zones() if a configuration change is detected
> (change in the number of zones or zone size). The function
> blk_revalidate_disk_zones() issues report_zones calls that are very
> large, that is, to obtain zone information for all zones of the disk
> with a single command. The size of the report zones command buffer
> necessary for such large request generally is lower than the disk
> max_hw_sectors and KMALLOC_MAX_SIZE (4MB) and succeeds on boot (no
> memory fragmentation), but often fail at run time (e.g. hot-plug
> event). This causes the disk revalidation to fail and the disk
> capacity to be changed to 0.
> 
> This problem can be avoided by using vmalloc() instead of kmalloc() for
> the buffer allocation. To limit the amount of memory to be allocated,
> this patch also introduces the arbitrary SD_ZBC_REPORT_MAX_ZONES
> maximum number of zones to report with a single report zones command.
> This limit may be lowered further to satisfy the disk max_hw_sectors
> limit. Finally, to ensure that the vmalloc-ed buffer can always be
> mapped in a request, the buffer size is further limited to at most
> queue_max_segments() pages, allowing successful mapping of the buffer
> even in the worst case scenario where none of the buffer pages are
> contiguous.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>

Re: [PATCH 3/3] block: Limit zone array allocation size

[Bart Van Assche]

On 6/24/19 7:46 PM, Damien Le Moal wrote:
> Limit the size of the struct blk_zone array used in
> blk_revalidate_disk_zones() to avoid memory allocation failures leading
> to disk revalidation failure. Further reduce the likelyhood of these
> failures by using kvmalloc() instead of directly allocating contiguous
> pages.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>

Re: [PATCH 1/3] block: Allow mapping of vmalloc-ed buffers

[Christoph Hellwig]

On Tue, Jun 25, 2019 at 11:46:23AM +0900, Damien Le Moal wrote:
> To allow the SCSI subsystem scsi_execute_req() function to issue
> requests using large buffers that are better allocated with vmalloc()
> rather than kmalloc(), modify bio_map_kern() to allow passing a buffer
> allocated with the vmalloc() function. To do so, simply test the buffer
> address using is_vmalloc_addr() and use vmalloc_to_page() instead of
> virt_to_page() to obtain the pages of vmalloc-ed buffers.

This is broken on architectures with VIVT caches.  You need to flush
and invalidate the caches based on the virtual address on those before
performing DMA operations.

Re: [PATCH 1/3] block: Allow mapping of vmalloc-ed buffers

[Damien Le Moal]

On 2019/06/26 1:06, Chaitanya Kulkarni wrote:
> On 06/25/2019 08:59 AM, Bart Van Assche wrote:
>> On 6/24/19 8:24 PM, Chaitanya Kulkarni wrote:
>>> nit:- Can we use is_vmalloc_addr() call directly so that
>>> "if (is_vmalloc)" ->  "if (is_vmalloc_addr(data))" and remove is_vmalloc
>>> variable.
>> That would change a single call of is_vmalloc_addr() into multiple?
> 
> Well is_vmalloc_addr() it is an in-line helper with address comparison.
> 
> is it too expensive to have such a comparison in the loop ?

Probably not, but I do not see the point in calling it for every page either
since the cost of the additional bool on the stack is likely also very low.

-- 
Damien Le Moal
Western Digital Research

Re: [PATCH 1/3] block: Allow mapping of vmalloc-ed buffers

[Chaitanya Kulkarni]

On 6/25/19 6:38 PM, Damien Le Moal wrote:
> On 2019/06/26 1:06, Chaitanya Kulkarni wrote:
>> On 06/25/2019 08:59 AM, Bart Van Assche wrote:
>>> On 6/24/19 8:24 PM, Chaitanya Kulkarni wrote:
>>>> nit:- Can we use is_vmalloc_addr() call directly so that
>>>> "if (is_vmalloc)" ->  "if (is_vmalloc_addr(data))" and remove is_vmalloc
>>>> variable.
>>> That would change a single call of is_vmalloc_addr() into multiple?
>>
>> Well is_vmalloc_addr() it is an in-line helper with address comparison.
>>
>> is it too expensive to have such a comparison in the loop ?
> 
> Probably not, but I do not see the point in calling it for every page either
> since the cost of the additional bool on the stack is likely also very low.
> 
Okay.