UBI: reduce memory consumption

Remove the pre-allocated 'peb_buf2' buffer because we do not really need it.
The only reason UBI has it is to check that the data were written correctly.
But we do not have to have 2 buffers for this and waste RAM - we can just
compare CRC checksums instead. This reduces UBI memory consumption.

Artem bityutskiy: massaged the patch and commit message

Signed-off-by: Josselin Costanzi <josselin.costanzi@mobile-devices.fr>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

3 files changed, 4 insertions, 12 deletions

diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 115749f20f9e..6e0806bff9f7 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -949,10 +949,6 @@ int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num, int vid_hdr_offset)
         if (!ubi->peb_buf1)
                 goto out_free;
 
-        ubi->peb_buf2 = vmalloc(ubi->peb_size);
-        if (!ubi->peb_buf2)
-                goto out_free;
-
         err = ubi_debugging_init_dev(ubi);
         if (err)
                 goto out_free;
@@ -1030,7 +1026,6 @@ out_debugging:
         ubi_debugging_exit_dev(ubi);
 out_free:
         vfree(ubi->peb_buf1);
-        vfree(ubi->peb_buf2);
         if (ref)
                 put_device(&ubi->dev);
         else
@@ -1102,7 +1097,6 @@ int ubi_detach_mtd_dev(int ubi_num, int anyway)
         put_mtd_device(ubi->mtd);
         ubi_debugging_exit_dev(ubi);
         vfree(ubi->peb_buf1);
-        vfree(ubi->peb_buf2);
         ubi_msg("mtd%d is detached from ubi%d", ubi->mtd->index, ubi->ubi_num);
         put_device(&ubi->dev);
         return 0;
diff --git a/drivers/mtd/ubi/eba.c b/drivers/mtd/ubi/eba.c
index cd26da8ad225..f548af3c98bb 100644
--- a/drivers/mtd/ubi/eba.c
+++ b/drivers/mtd/ubi/eba.c
@@ -1134,8 +1134,8 @@ int ubi_eba_copy_leb(struct ubi_device *ubi, int from, int to,
                  * We've written the data and are going to read it back to make
                  * sure it was written correctly.
                  */
-
-                err = ubi_io_read_data(ubi, ubi->peb_buf2, to, 0, aldata_size);
+                memset(ubi->peb_buf1, 0xFF, aldata_size);
+                err = ubi_io_read_data(ubi, ubi->peb_buf1, to, 0, aldata_size);
                 if (err) {
                         if (err != UBI_IO_BITFLIPS) {
                                 ubi_warn("error %d while reading data back "
@@ -1149,7 +1149,7 @@ int ubi_eba_copy_leb(struct ubi_device *ubi, int from, int to,
 
                 cond_resched();
 
-                if (memcmp(ubi->peb_buf1, ubi->peb_buf2, aldata_size)) {
+                if (crc != crc32(UBI_CRC32_INIT, ubi->peb_buf1, data_size)) {
                         ubi_warn("read data back from PEB %d and it is "
                                  "different", to);
                         err = -EINVAL;
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index d51d75d34446..cb93ad97468b 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -388,8 +388,7 @@ struct ubi_wl_entry;
  * @mtd: MTD device descriptor
  *
  * @peb_buf1: a buffer of PEB size used for different purposes
- * @peb_buf2: another buffer of PEB size used for different purposes
- * @buf_mutex: protects @peb_buf1 and @peb_buf2
+ * @buf_mutex: protects @peb_buf1
  * @ckvol_mutex: serializes static volume checking when opening
  *
  * @dbg: debugging information for this UBI device
@@ -472,7 +471,6 @@ struct ubi_device {
         struct mtd_info *mtd;
 
         void *peb_buf1;
-        void *peb_buf2;
         struct mutex buf_mutex;
         struct mutex ckvol_mutex;