UBIFS: improve statfs reporting even more

Since free space we report in statfs is file size which should
fit to the FS - change the way we calculate free space and use
leb_overhead instead of dark_wm in calculations.

Results of "freespace" test (120MiB volume, 16KiB LEB size,
512 bytes page size). Before the change:

freespace: Test 1: fill the space we have 3 times
freespace: was free: 85204992 bytes 81.3 MiB, wrote: 96489472 bytes 92.0 MiB, delta: 11284480 bytes 10.8 MiB, wrote 13.2% more than predicted
freespace: was free: 83554304 bytes 79.7 MiB, wrote: 96489472 bytes 92.0 MiB, delta: 12935168 bytes 12.3 MiB, wrote 15.5% more than predicted
freespace: was free: 83554304 bytes 79.7 MiB, wrote: 96493568 bytes 92.0 MiB, delta: 12939264 bytes 12.3 MiB, wrote 15.5% more than predicted
freespace: Test 1 finished

freespace: Test 2: gradually lessen amount of free space and fill the FS
freespace: do 10 steps, lessen free space by 7596218 bytes 7.2 MiB each time
freespace: was free: 78675968 bytes 75.0 MiB, wrote: 88903680 bytes 84.8 MiB, delta: 10227712 bytes 9.8 MiB, wrote 13.0% more than predicted
freespace: was free: 72015872 bytes 68.7 MiB, wrote: 81514496 bytes 77.7 MiB, delta: 9498624 bytes 9.1 MiB, wrote 13.2% more than predicted
freespace: was free: 63938560 bytes 61.0 MiB, wrote: 72589312 bytes 69.2 MiB, delta: 8650752 bytes 8.2 MiB, wrote 13.5% more than predicted
freespace: was free: 56127488 bytes 53.5 MiB, wrote: 63762432 bytes 60.8 MiB, delta: 7634944 bytes 7.3 MiB, wrote 13.6% more than predicted
freespace: was free: 48336896 bytes 46.1 MiB, wrote: 54935552 bytes 52.4 MiB, delta: 6598656 bytes 6.3 MiB, wrote 13.7% more than predicted
freespace: was free: 40587264 bytes 38.7 MiB, wrote: 46157824 bytes 44.0 MiB, delta: 5570560 bytes 5.3 MiB, wrote 13.7% more than predicted
freespace: was free: 32841728 bytes 31.3 MiB, wrote: 37384192 bytes 35.7 MiB, delta: 4542464 bytes 4.3 MiB, wrote 13.8% more than predicted
freespace: was free: 25100288 bytes 23.9 MiB, wrote: 28618752 bytes 27.3 MiB, delta: 3518464 bytes 3.4 MiB, wrote 14.0% more than predicted
freespace: was free: 17342464 bytes 16.5 MiB, wrote: 19841024 bytes 18.9 MiB, delta: 2498560 bytes 2.4 MiB, wrote 14.4% more than predicted
freespace: was free: 9605120 bytes 9.2 MiB, wrote: 11063296 bytes 10.6 MiB, delta: 1458176 bytes 1.4 MiB, wrote 15.2% more than predicted
freespace: Test 2 finished

freespace: Test 3: gradually lessen amount of free space by trashing and fill the FS
freespace: do 10 steps, lessen free space by 7606272 bytes 7.3 MiB each time
freespace: trashing: was free: 83668992 bytes 79.8 MiB, need free: 7606272 bytes 7.3 MiB, files created: 248297, delete 225724 (90.9% of them)
freespace: was free: 70803456 bytes 67.5 MiB, wrote: 82485248 bytes 78.7 MiB, delta: 11681792 bytes 11.1 MiB, wrote 16.5% more than predicted
freespace: trashing: was free: 81080320 bytes 77.3 MiB, need free: 15212544 bytes 14.5 MiB, files created: 248711, delete 202047 (81.2% of them)
freespace: was free: 59867136 bytes 57.1 MiB, wrote: 71897088 bytes 68.6 MiB, delta: 12029952 bytes 11.5 MiB, wrote 20.1% more than predicted
freespace: trashing: was free: 82243584 bytes 78.4 MiB, need free: 22818816 bytes 21.8 MiB, files created: 248866, delete 179817 (72.3% of them)
freespace: was free: 50905088 bytes 48.5 MiB, wrote: 63168512 bytes 60.2 MiB, delta: 12263424 bytes 11.7 MiB, wrote 24.1% more than predicted
freespace: trashing: was free: 83402752 bytes 79.5 MiB, need free: 30425088 bytes 29.0 MiB, files created: 248920, delete 158114 (63.5% of them)
freespace: was free: 42651648 bytes 40.7 MiB, wrote: 55406592 bytes 52.8 MiB, delta: 12754944 bytes 12.2 MiB, wrote 29.9% more than predicted
freespace: trashing: was free: 84402176 bytes 80.5 MiB, need free: 38031360 bytes 36.3 MiB, files created: 248709, delete 136641 (54.9% of them)
freespace: was free: 35233792 bytes 33.6 MiB, wrote: 48250880 bytes 46.0 MiB, delta: 13017088 bytes 12.4 MiB, wrote 36.9% more than predicted
freespace: trashing: was free: 82530304 bytes 78.7 MiB, need free: 45637632 bytes 43.5 MiB, files created: 248778, delete 111208 (44.7% of them)
freespace: was free: 27287552 bytes 26.0 MiB, wrote: 40267776 bytes 38.4 MiB, delta: 12980224 bytes 12.4 MiB, wrote 47.6% more than predicted
freespace: trashing: was free: 85114880 bytes 81.2 MiB, need free: 53243904 bytes 50.8 MiB, files created: 248508, delete 93052 (37.4% of them)
freespace: was free: 22437888 bytes 21.4 MiB, wrote: 35328000 bytes 33.7 MiB, delta: 12890112 bytes 12.3 MiB, wrote 57.4% more than predicted
freespace: trashing: was free: 84103168 bytes 80.2 MiB, need free: 60850176 bytes 58.0 MiB, files created: 248637, delete 68743 (27.6% of them)
freespace: was free: 15536128 bytes 14.8 MiB, wrote: 28319744 bytes 27.0 MiB, delta: 12783616 bytes 12.2 MiB, wrote 82.3% more than predicted
freespace: trashing: was free: 84357120 bytes 80.4 MiB, need free: 68456448 bytes 65.3 MiB, files created: 248567, delete 46852 (18.8% of them)
freespace: was free: 9015296 bytes 8.6 MiB, wrote: 22044672 bytes 21.0 MiB, delta: 13029376 bytes 12.4 MiB, wrote 144.5% more than predicted
freespace: trashing: was free: 84942848 bytes 81.0 MiB, need free: 76062720 bytes 72.5 MiB, files created: 248636, delete 25993 (10.5% of them)
freespace: was free: 6086656 bytes 5.8 MiB, wrote: 8331264 bytes 7.9 MiB, delta: 2244608 bytes 2.1 MiB, wrote 36.9% more than predicted
freespace: Test 3 finished

freespace: finished successfully

After the change:

freespace: Test 1: fill the space we have 3 times
freespace: was free: 94048256 bytes 89.7 MiB, wrote: 96489472 bytes 92.0 MiB, delta: 2441216 bytes 2.3 MiB, wrote 2.6% more than predicted
freespace: was free: 92246016 bytes 88.0 MiB, wrote: 96493568 bytes 92.0 MiB, delta: 4247552 bytes 4.1 MiB, wrote 4.6% more than predicted
freespace: was free: 92254208 bytes 88.0 MiB, wrote: 96489472 bytes 92.0 MiB, delta: 4235264 bytes 4.0 MiB, wrote 4.6% more than predicted
freespace: Test 1 finished

freespace: Test 2: gradually lessen amount of free space and fill the FS
freespace: do 10 steps, lessen free space by 8386001 bytes 8.0 MiB each time
freespace: was free: 86605824 bytes 82.6 MiB, wrote: 88252416 bytes 84.2 MiB, delta: 1646592 bytes 1.6 MiB, wrote 1.9% more than predicted
freespace: was free: 78667776 bytes 75.0 MiB, wrote: 80715776 bytes 77.0 MiB, delta: 2048000 bytes 2.0 MiB, wrote 2.6% more than predicted
freespace: was free: 69615616 bytes 66.4 MiB, wrote: 71630848 bytes 68.3 MiB, delta: 2015232 bytes 1.9 MiB, wrote 2.9% more than predicted
freespace: was free: 61018112 bytes 58.2 MiB, wrote: 62783488 bytes 59.9 MiB, delta: 1765376 bytes 1.7 MiB, wrote 2.9% more than predicted
freespace: was free: 52424704 bytes 50.0 MiB, wrote: 53968896 bytes 51.5 MiB, delta: 1544192 bytes 1.5 MiB, wrote 2.9% more than predicted
freespace: was free: 43880448 bytes 41.8 MiB, wrote: 45199360 bytes 43.1 MiB, delta: 1318912 bytes 1.3 MiB, wrote 3.0% more than predicted
freespace: was free: 35332096 bytes 33.7 MiB, wrote: 36425728 bytes 34.7 MiB, delta: 1093632 bytes 1.0 MiB, wrote 3.1% more than predicted
freespace: was free: 26771456 bytes 25.5 MiB, wrote: 27643904 bytes 26.4 MiB, delta: 872448 bytes 852.0 KiB, wrote 3.3% more than predicted
freespace: was free: 18231296 bytes 17.4 MiB, wrote: 18878464 bytes 18.0 MiB, delta: 647168 bytes 632.0 KiB, wrote 3.5% more than predicted
freespace: was free: 9674752 bytes 9.2 MiB, wrote: 10088448 bytes 9.6 MiB, delta: 413696 bytes 404.0 KiB, wrote 4.3% more than predicted
freespace: Test 2 finished

freespace: Test 3: gradually lessen amount of free space by trashing and fill the FS
freespace: do 10 steps, lessen free space by 8397544 bytes 8.0 MiB each time
freespace: trashing: was free: 92372992 bytes 88.1 MiB, need free: 8397552 bytes 8.0 MiB, files created: 248296, delete 225723 (90.9% of them)
freespace: was free: 71909376 bytes 68.6 MiB, wrote: 82472960 bytes 78.7 MiB, delta: 10563584 bytes 10.1 MiB, wrote 14.7% more than predicted
freespace: trashing: was free: 88989696 bytes 84.9 MiB, need free: 16795096 bytes 16.0 MiB, files created: 248794, delete 201838 (81.1% of them)
freespace: was free: 60354560 bytes 57.6 MiB, wrote: 71782400 bytes 68.5 MiB, delta: 11427840 bytes 10.9 MiB, wrote 18.9% more than predicted
freespace: trashing: was free: 90304512 bytes 86.1 MiB, need free: 25192640 bytes 24.0 MiB, files created: 248733, delete 179342 (72.1% of them)
freespace: was free: 51187712 bytes 48.8 MiB, wrote: 62943232 bytes 60.0 MiB, delta: 11755520 bytes 11.2 MiB, wrote 23.0% more than predicted
freespace: trashing: was free: 91209728 bytes 87.0 MiB, need free: 33590184 bytes 32.0 MiB, files created: 248779, delete 157160 (63.2% of them)
freespace: was free: 42704896 bytes 40.7 MiB, wrote: 55050240 bytes 52.5 MiB, delta: 12345344 bytes 11.8 MiB, wrote 28.9% more than predicted
freespace: trashing: was free: 92700672 bytes 88.4 MiB, need free: 41987728 bytes 40.0 MiB, files created: 248848, delete 136135 (54.7% of them)
freespace: was free: 35250176 bytes 33.6 MiB, wrote: 48115712 bytes 45.9 MiB, delta: 12865536 bytes 12.3 MiB, wrote 36.5% more than predicted
freespace: trashing: was free: 93986816 bytes 89.6 MiB, need free: 50385272 bytes 48.1 MiB, files created: 248723, delete 115385 (46.4% of them)
freespace: was free: 29995008 bytes 28.6 MiB, wrote: 41582592 bytes 39.7 MiB, delta: 11587584 bytes 11.1 MiB, wrote 38.6% more than predicted
freespace: trashing: was free: 91881472 bytes 87.6 MiB, need free: 58782816 bytes 56.1 MiB, files created: 248645, delete 89569 (36.0% of them)
freespace: was free: 22511616 bytes 21.5 MiB, wrote: 34705408 bytes 33.1 MiB, delta: 12193792 bytes 11.6 MiB, wrote 54.2% more than predicted
freespace: trashing: was free: 91774976 bytes 87.5 MiB, need free: 67180360 bytes 64.1 MiB, files created: 248580, delete 66616 (26.8% of them)
freespace: was free: 16908288 bytes 16.1 MiB, wrote: 26898432 bytes 25.7 MiB, delta: 9990144 bytes 9.5 MiB, wrote 59.1% more than predicted
freespace: trashing: was free: 92450816 bytes 88.2 MiB, need free: 75577904 bytes 72.1 MiB, files created: 248654, delete 45381 (18.3% of them)
freespace: was free: 10170368 bytes 9.7 MiB, wrote: 19111936 bytes 18.2 MiB, delta: 8941568 bytes 8.5 MiB, wrote 87.9% more than predicted
freespace: trashing: was free: 93282304 bytes 89.0 MiB, need free: 83975448 bytes 80.1 MiB, files created: 248513, delete 24794 (10.0% of them)
freespace: was free: 3911680 bytes 3.7 MiB, wrote: 7872512 bytes 7.5 MiB, delta: 3960832 bytes 3.8 MiB, wrote 101.3% more than predicted
freespace: Test 3 finished

freespace: finished successfully

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

fs/ubifs/budget.c

@@ -747,14 +747,24 @@ long long ubifs_reported_space(const struct ubifs_info *c, uint64_t free)
 }
 
 /**
- * ubifs_budg_get_free_space - return amount of free space.
+ * ubifs_get_free_space - return amount of free space.
  * @c: UBIFS file-system description object
  *
- * This function returns amount of free space on the file-system.
+ * This function calculates amount of free space to report to user-space.
+ *
+ * Because UBIFS may introduce substantial overhead (the index, node headers,
+ * alighment, wastage at the end of eraseblocks, etc), it cannot report real
+ * amount of free flash space it has (well, because not all dirty space is
+ * reclamable, UBIFS does not actually know the real amount). If UBIFS did so,
+ * it would bread user expectetion about what free space is. Users seem to
+ * accustomed to assume that if the file-system reports N bytes of free space,
+ * they would be able to fit a file of N bytes to the FS. This almost works for
+ * traditional file-systems, because they have way less overhead than UBIFS.
+ * So, to keep users happy, UBIFS tries to take the overhead into account.
  */
-long long ubifs_budg_get_free_space(struct ubifs_info *c)
+long long ubifs_get_free_space(struct ubifs_info *c)
 {
-	int min_idx_lebs;
+	int min_idx_lebs, rsvd_idx_lebs, lebs;
 	long long available, outstanding, free;
 
 	spin_lock(&c->space_lock);
@@ -771,6 +781,26 @@ long long ubifs_budg_get_free_space(struct ubifs_info *c)
 	}
 
 	available = ubifs_calc_available(c, min_idx_lebs);
+
+	/*
+	 * When reporting free space to user-space, UBIFS guarantees that it is
+	 * possible to write a file of free space size. This means that for
+	 * empty LEBs we may use more precise calculations than
+	 * 'ubifs_calc_available()' is using. Namely, we know that in empty
+	 * LEBs we would waste only @c->leb_overhead bytes, not @c->dark_wm.
+	 * Thus, amend the available space.
+	 *
+	 * Note, the calculations below are similar to what we have in
+	 * 'do_budget_space()', so refer there for comments.
+	 */
+	if (min_idx_lebs > c->lst.idx_lebs)
+		rsvd_idx_lebs = min_idx_lebs - c->lst.idx_lebs;
+	else
+		rsvd_idx_lebs = 0;
+	lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
+	       c->lst.taken_empty_lebs;
+	lebs -= rsvd_idx_lebs;
+	available += lebs * (c->dark_wm - c->leb_overhead);
 	spin_unlock(&c->space_lock);
 
 	if (available > outstanding)

fs/ubifs/super.c

@@ -371,7 +371,7 @@ static int ubifs_statfs(struct dentry *dentry, struct kstatfs *buf)
 	struct ubifs_info *c = dentry->d_sb->s_fs_info;
 	unsigned long long free;
 
-	free = ubifs_budg_get_free_space(c);
+	free = ubifs_get_free_space(c);
 	dbg_gen("free space %lld bytes (%lld blocks)",
 		free, free >> UBIFS_BLOCK_SHIFT);
 
@@ -653,11 +653,11 @@ static int init_constants_late(struct ubifs_info *c)
 	 * internally because it does not make much sense for UBIFS, but it is
 	 * necessary to report something for the 'statfs()' call.
 	 *
-	 * Subtract the LEB reserved for GC and the LEB which is reserved for
-	 * deletions.
+	 * Subtract the LEB reserved for GC, the LEB which is reserved for
+	 * deletions, and assume only one journal head is available.
 	 */
-	tmp64 = c->main_lebs - 2;
-	tmp64 *= (uint64_t)c->leb_size - c->dark_wm;
+	tmp64 = c->main_lebs - 2 - c->jhead_cnt + 1;
+	tmp64 *= (uint64_t)c->leb_size - c->leb_overhead;
 	tmp64 = ubifs_reported_space(c, tmp64);
 	c->block_cnt = tmp64 >> UBIFS_BLOCK_SHIFT;
 

fs/ubifs/ubifs.h

@@ -1443,7 +1443,7 @@ void ubifs_release_ino_dirty(struct ubifs_info *c, struct inode *inode,
 				struct ubifs_budget_req *req);
 void ubifs_cancel_ino_op(struct ubifs_info *c, struct inode *inode,
 			 struct ubifs_budget_req *req);
-long long ubifs_budg_get_free_space(struct ubifs_info *c);
+long long ubifs_get_free_space(struct ubifs_info *c);
 int ubifs_calc_min_idx_lebs(struct ubifs_info *c);
 void ubifs_convert_page_budget(struct ubifs_info *c);
 long long ubifs_reported_space(const struct ubifs_info *c, uint64_t free);