readahead: bump a device's request_nr when enabling readahead

src/readahead-common.c

@@ -20,7 +20,6 @@
 ***/
 
 #include <errno.h>
-#include <libudev.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/sysinfo.h>
@@ -28,6 +27,7 @@
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <unistd.h>
+#include <libudev.h>
 
 #include "log.h"
 #include "readahead-common.h"
@@ -68,6 +68,9 @@ int fs_on_ssd(const char *p) {
         if (stat(p, &st) < 0)
                 return -errno;
 
+        if (major(st.st_dev) == 0)
+                return false;
+
         if (!(udev = udev_new()))
                 return -ENOMEM;
 
@@ -170,3 +173,75 @@ finish:
 
         return m;
 }
+
+
+#define BUMP_REQUEST_NR (16*1024)
+
+int bump_request_nr(const char *p) {
+        struct stat st;
+        struct udev *udev = NULL;
+        struct udev_device *udev_device = NULL, *look_at = NULL;
+        const char *nr_requests;
+        uint64_t u;
+        char nr[64], *ap = NULL;
+        int r;
+
+        assert(p);
+
+        if (stat(p, &st) < 0)
+                return -errno;
+
+        if (major(st.st_dev) == 0)
+                return 0;
+
+        if (!(udev = udev_new()))
+                return -ENOMEM;
+
+        if (!(udev_device = udev_device_new_from_devnum(udev, 'b', st.st_dev))) {
+                r = -ENOENT;
+                goto finish;
+        }
+
+        look_at = udev_device;
+        if (!(nr_requests = udev_device_get_sysattr_value(look_at, "queue/nr_requests"))) {
+
+                /* Hmm, if the block device doesn't have a queue
+                 * subdir, the let's look in the parent */
+                look_at = udev_device_get_parent(udev_device);
+                nr_requests = udev_device_get_sysattr_value(look_at, "queue/nr_requests");
+        }
+
+        if (!nr_requests) {
+                r = -ENOENT;
+                goto finish;
+        }
+
+        if (safe_atou64(nr_requests, &u) >= 0 && u >= BUMP_REQUEST_NR) {
+                r = 0;
+                goto finish;
+        }
+
+        if (asprintf(&ap, "%s/queue/nr_requests", udev_device_get_syspath(look_at)) < 0) {
+                r = -ENOMEM;
+                goto finish;
+        }
+
+        snprintf(nr, sizeof(nr), "%lu", (unsigned long) BUMP_REQUEST_NR);
+
+        if ((r = write_one_line_file(ap, nr)) < 0)
+                goto finish;
+
+        log_info("Bumped block_nr parameter of %s to %lu. This is a temporary hack and should be removed one day.", udev_device_get_devnode(look_at), (unsigned long) BUMP_REQUEST_NR);
+        r = 1;
+
+finish:
+        if (udev_device)
+                udev_device_unref(udev_device);
+
+        if (udev)
+                udev_unref(udev);
+
+        free(ap);
+
+        return r;
+}

src/readahead-common.h

@@ -44,4 +44,6 @@ typedef struct ReadaheadShared {
 
 ReadaheadShared *shared_get(void);
 
+int bump_request_nr(const char *p);
+
 #endif

src/readahead-replay.c

@@ -127,6 +127,7 @@ static int replay(const char *root) {
         assert(root);
 
         write_one_line_file("/proc/self/oom_score_adj", "1000");
+        bump_request_nr(root);
 
         if (asprintf(&pack_fn, "%s/.readahead", root) < 0) {
                 log_error("Out of memory");