USB: gadget: f_mass_storage: Flush writes after every 4 MB.

This avoids excessive caching at the block level layer when copying large
files to the storage device.

Signed-off-by: Mike Lockwood <lockwood@android.com>

diff --git a/drivers/usb/gadget/f_mass_storage.c b/drivers/usb/gadget/f_mass_storage.c
index 1dc72346b81b2214ff0972005896a1f73568c527..6fccd710217bcce61c0400a9287c3138098edaf6 100644 (file)
--- a/drivers/usb/gadget/f_mass_storage.c
+++ b/drivers/usb/gadget/f_mass_storage.c
@@ -79,6 +79,9 @@
 
 #define BULK_BUFFER_SIZE           4096
 
+/* flush after every 4 meg of writes to avoid excessive block level caching */
+#define MAX_UNFLUSHED_BYTES (4 * 1024 * 1024)
+
 /*-------------------------------------------------------------------------*/
 
 #define DRIVER_NAME            "usb_mass_storage"
@@ -226,6 +229,7 @@ struct lun {
        struct file     *filp;
        loff_t          file_length;
        loff_t          num_sectors;
+       unsigned int unflushed_bytes;
 
        unsigned int    ro : 1;
        unsigned int    prevent_medium_removal : 1;
@@ -392,7 +396,7 @@ static struct fsg_dev                       *the_fsg;
 
 static void    close_backing_file(struct fsg_dev *fsg, struct lun *curlun);
 static void    close_all_backing_files(struct fsg_dev *fsg);
-
+static int fsync_sub(struct lun *curlun);
 
 /*-------------------------------------------------------------------------*/
 
@@ -1039,6 +1043,13 @@ static int do_write(struct fsg_dev *fsg)
                        amount_left_to_write -= nwritten;
                        fsg->residue -= nwritten;
 
+#ifdef MAX_UNFLUSHED_BYTES
+                       curlun->unflushed_bytes += nwritten;
+                       if (curlun->unflushed_bytes >= MAX_UNFLUSHED_BYTES) {
+                               fsync_sub(curlun);
+                               curlun->unflushed_bytes = 0;
+                       }
+#endif
                        /* If an error occurred, report it and its position */
                        if (nwritten < amount) {
                                curlun->sense_data = SS_WRITE_ERROR;
@@ -2515,6 +2526,7 @@ static int open_backing_file(struct fsg_dev *fsg, struct lun *curlun,
        curlun->ro = ro;
        curlun->filp = filp;
        curlun->file_length = size;
+       curlun->unflushed_bytes = 0;
        curlun->num_sectors = num_sectors;
        LDBG(curlun, "open backing file: %s size: %lld num_sectors: %lld\n",
                        filename, size, num_sectors);