drbd: allow petabyte storage on 64bit arch

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

1 files changed, 106 insertions, 64 deletions

diff --git a/drivers/block/drbd/drbd_bitmap.c b/drivers/block/drbd/drbd_bitmap.c
index 72cd41a96ef9..0e31e573af72 100644
--- a/drivers/block/drbd/drbd_bitmap.c
+++ b/drivers/block/drbd/drbd_bitmap.c
@@ -37,10 +37,46 @@
  * convention:
  * function name drbd_bm_... => used elsewhere, "public".
  * function name      bm_... => internal to implementation, "private".
+ */
+
 
- * Note that since find_first_bit returns int, at the current granularity of
- * the bitmap (4KB per byte), this implementation "only" supports up to
- * 1<<(32+12) == 16 TB...
+/*
+ * LIMITATIONS:
+ * We want to support >= peta byte of backend storage, while for now still using
+ * a granularity of one bit per 4KiB of storage.
+ * 1 << 50              bytes backend storage (1 PiB)
+ * 1 << (50 - 12)       bits needed
+ *      38 --> we need u64 to index and count bits
+ * 1 << (38 - 3)        bitmap bytes needed
+ *      35 --> we still need u64 to index and count bytes
+ *                      (that's 32 GiB of bitmap for 1 PiB storage)
+ * 1 << (35 - 2)        32bit longs needed
+ *      33 --> we'd even need u64 to index and count 32bit long words.
+ * 1 << (35 - 3)        64bit longs needed
+ *      32 --> we could get away with a 32bit unsigned int to index and count
+ *      64bit long words, but I rather stay with unsigned long for now.
+ *      We probably should neither count nor point to bytes or long words
+ *      directly, but either by bitnumber, or by page index and offset.
+ * 1 << (35 - 12)
+ *      22 --> we need that much 4KiB pages of bitmap.
+ *      1 << (22 + 3) --> on a 64bit arch,
+ *      we need 32 MiB to store the array of page pointers.
+ *
+ * Because I'm lazy, and because the resulting patch was too large, too ugly
+ * and still incomplete, on 32bit we still "only" support 16 TiB (minus some),
+ * (1 << 32) bits * 4k storage.
+ *
+
+ * bitmap storage and IO:
+ *      Bitmap is stored little endian on disk, and is kept little endian in
+ *      core memory. Currently we still hold the full bitmap in core as long
+ *      as we are "attached" to a local disk, which at 32 GiB for 1PiB storage
+ *      seems excessive.
+ *
+ *      We plan to reduce the amount of in-core bitmap pages by pageing them in
+ *      and out against their on-disk location as necessary, but need to make
+ *      sure we don't cause too much meta data IO, and must not deadlock in
+ *      tight memory situations. This needs some more work.
  */
 
 /*
@@ -56,13 +92,9 @@
 struct drbd_bitmap {
         struct page **bm_pages;
         spinlock_t bm_lock;
-        /* WARNING unsigned long bm_*:
-         * 32bit number of bit offset is just enough for 512 MB bitmap.
-         * it will blow up if we make the bitmap bigger...
-         * not that it makes much sense to have a bitmap that large,
-         * rather change the granularity to 16k or 64k or something.
-         * (that implies other problems, however...)
-         */
+
+        /* see LIMITATIONS: above */
+
         unsigned long bm_set;       /* nr of set bits; THINK maybe atomic_t? */
         unsigned long bm_bits;
         size_t   bm_words;
@@ -517,43 +549,39 @@ static void bm_set_surplus(struct drbd_bitmap *b)
         bm_unmap(p_addr);
 }
 
+/* you better not modify the bitmap while this is running,
+ * or its results will be stale */
 static unsigned long bm_count_bits(struct drbd_bitmap *b)
 {
-        unsigned long *p_addr, *bm, offset = 0;
+        unsigned long *p_addr;
         unsigned long bits = 0;
-        unsigned long i, do_now;
-        unsigned long words;
-
-        /* due to 64bit alignment, the last long on a 32bit arch
-         * may be not used at all. The last used long will likely
-         * be only partially used, always. Don't count those bits,
-         * but mask them out. */
-        words = (b->bm_bits + BITS_PER_LONG - 1) >> LN2_BPL;
-
-        while (offset < words) {
-                i = do_now = min_t(size_t, words-offset, LWPP);
-                p_addr = __bm_map_pidx(b, bm_word_to_page_idx(b, offset), KM_USER0);
-                bm = p_addr + MLPP(offset);
-                while (i--) {
-                        bits += hweight_long(*bm++);
-                }
-                offset += do_now;
-                if (offset == words) {
-                        /* last word may only be partially used,
-                         * see also bm_clear_surplus. */
-                        i = (1UL << (b->bm_bits & (BITS_PER_LONG-1))) -1;
-                        if (i) {
-                                bits -= hweight_long(p_addr[do_now-1] & ~i);
-                                p_addr[do_now-1] &= i;
-                        }
-                        /* 32bit arch, may have an unused padding long */
-                        if (words != b->bm_words)
-                                p_addr[do_now] = 0;
-                }
+        unsigned long mask = (1UL << (b->bm_bits & BITS_PER_LONG_MASK)) -1;
+        int idx, last_page, i, last_word;
+
+        /* because of the "extra long to catch oob access" we allocate in
+         * drbd_bm_resize, bm_number_of_pages -1 is not necessarily the page
+         * containing the last _relevant_ bitmap word */
+        last_page = bm_bit_to_page_idx(b, b->bm_bits-1);
+
+        /* all but last page */
+        for (idx = 0; idx < last_page; idx++) {
+                p_addr = __bm_map_pidx(b, idx, KM_USER0);
+                for (i = 0; i < LWPP; i++)
+                        bits += hweight_long(p_addr[i]);
                 __bm_unmap(p_addr, KM_USER0);
                 cond_resched();
         }
-
+        /* last (or only) page */
+        last_word = ((b->bm_bits - 1) & BITS_PER_PAGE_MASK) >> LN2_BPL;
+        p_addr = __bm_map_pidx(b, idx, KM_USER0);
+        for (i = 0; i < last_word; i++)
+                bits += hweight_long(p_addr[i]);
+        p_addr[last_word] &= cpu_to_lel(mask);
+        bits += hweight_long(p_addr[last_word]);
+        /* 32bit arch, may have an unused padding long */
+        if (BITS_PER_LONG == 32 && (last_word & 1) == 0)
+                p_addr[last_word+1] = 0;
+        __bm_unmap(p_addr, KM_USER0);
         return bits;
 }
 
@@ -564,8 +592,6 @@ static void bm_memset(struct drbd_bitmap *b, size_t offset, int c, size_t len)
         unsigned int idx;
         size_t do_now, end;
 
-#define BM_SECTORS_PER_BIT (BM_BLOCK_SIZE/512)
-
         end = offset + len;
 
         if (end > b->bm_words) {
@@ -645,8 +671,14 @@ int drbd_bm_resize(struct drbd_conf *mdev, sector_t capacity, int set_new_bits)
         words = ALIGN(bits, 64) >> LN2_BPL;
 
         if (get_ldev(mdev)) {
-                D_ASSERT((u64)bits <= (((u64)mdev->ldev->md.md_size_sect-MD_BM_OFFSET) << 12));
+                u64 bits_on_disk = ((u64)mdev->ldev->md.md_size_sect-MD_BM_OFFSET) << 12;
                 put_ldev(mdev);
+                if (bits > bits_on_disk) {
+                        dev_info(DEV, "bits = %lu\n", bits);
+                        dev_info(DEV, "bits_on_disk = %llu\n", bits_on_disk);
+                        err = -ENOSPC;
+                        goto out;
+                }
         }
 
         /* one extra long to catch off by one errors */
@@ -1113,9 +1145,12 @@ int drbd_bm_write_lazy(struct drbd_conf *mdev, unsigned upper_idx) __must_hold(l
  * @mdev:       DRBD device.
  * @idx:        bitmap page index
  *
- * We don't want to special case on logical_block_size of the underlaying
- * device, so we submit PAGE_SIZE aligned pieces containing the requested enr.
+ * We don't want to special case on logical_block_size of the backend device,
+ * so we submit PAGE_SIZE aligned pieces.
  * Note that on "most" systems, PAGE_SIZE is 4k.
+ *
+ * In case this becomes an issue on systems with larger PAGE_SIZE,
+ * we may want to change this again to write 4k aligned 4k pieces.
  */
 int drbd_bm_write_page(struct drbd_conf *mdev, unsigned int idx) __must_hold(local)
 {
@@ -1144,52 +1179,57 @@ int drbd_bm_write_page(struct drbd_conf *mdev, unsigned int idx) __must_hold(loc
 
 /* NOTE
  * find_first_bit returns int, we return unsigned long.
- * should not make much difference anyways, but ...
+ * For this to work on 32bit arch with bitnumbers > (1<<32),
+ * we'd need to return u64, and get a whole lot of other places
+ * fixed where we still use unsigned long.
  *
  * this returns a bit number, NOT a sector!
  */
-#define BPP_MASK ((1UL << (PAGE_SHIFT+3)) - 1)
 static unsigned long __bm_find_next(struct drbd_conf *mdev, unsigned long bm_fo,
         const int find_zero_bit, const enum km_type km)
 {
         struct drbd_bitmap *b = mdev->bitmap;
-        unsigned long i = -1UL;
         unsigned long *p_addr;
-        unsigned long bit_offset; /* bit offset of the mapped page. */
+        unsigned long bit_offset;
+        unsigned i;
+
 
         if (bm_fo > b->bm_bits) {
                 dev_err(DEV, "bm_fo=%lu bm_bits=%lu\n", bm_fo, b->bm_bits);
+                bm_fo = DRBD_END_OF_BITMAP;
         } else {
                 while (bm_fo < b->bm_bits) {
                         /* bit offset of the first bit in the page */
-                        bit_offset = bm_fo & ~BPP_MASK;
+                        bit_offset = bm_fo & ~BITS_PER_PAGE_MASK;
                         p_addr = __bm_map_pidx(b, bm_bit_to_page_idx(b, bm_fo), km);
 
                         if (find_zero_bit)
-                                i = generic_find_next_zero_le_bit(p_addr, PAGE_SIZE*8, bm_fo & BPP_MASK);
+                                i = generic_find_next_zero_le_bit(p_addr,
+                                                PAGE_SIZE*8, bm_fo & BITS_PER_PAGE_MASK);
                         else
-                                i = generic_find_next_le_bit(p_addr, PAGE_SIZE*8, bm_fo & BPP_MASK);
+                                i = generic_find_next_le_bit(p_addr,
+                                                PAGE_SIZE*8, bm_fo & BITS_PER_PAGE_MASK);
 
                         __bm_unmap(p_addr, km);
                         if (i < PAGE_SIZE*8) {
-                                i = bit_offset + i;
-                                if (i >= b->bm_bits)
+                                bm_fo = bit_offset + i;
+                                if (bm_fo >= b->bm_bits)
                                         break;
                                 goto found;
                         }
                         bm_fo = bit_offset + PAGE_SIZE*8;
                 }
-                i = -1UL;
+                bm_fo = DRBD_END_OF_BITMAP;
         }
  found:
-        return i;
+        return bm_fo;
 }
 
 static unsigned long bm_find_next(struct drbd_conf *mdev,
         unsigned long bm_fo, const int find_zero_bit)
 {
         struct drbd_bitmap *b = mdev->bitmap;
-        unsigned long i = -1UL;
+        unsigned long i = DRBD_END_OF_BITMAP;
 
         ERR_IF(!b) return i;
         ERR_IF(!b->bm_pages) return i;
@@ -1267,9 +1307,9 @@ static int __bm_change_bits_to(struct drbd_conf *mdev, const unsigned long s,
                         last_page_nr = page_nr;
                 }
                 if (val)
-                        c += (0 == generic___test_and_set_le_bit(bitnr & BPP_MASK, p_addr));
+                        c += (0 == generic___test_and_set_le_bit(bitnr & BITS_PER_PAGE_MASK, p_addr));
                 else
-                        c -= (0 != generic___test_and_clear_le_bit(bitnr & BPP_MASK, p_addr));
+                        c -= (0 != generic___test_and_clear_le_bit(bitnr & BITS_PER_PAGE_MASK, p_addr));
         }
         if (p_addr)
                 __bm_unmap(p_addr, km);
@@ -1418,7 +1458,7 @@ int drbd_bm_test_bit(struct drbd_conf *mdev, const unsigned long bitnr)
                 bm_print_lock_info(mdev);
         if (bitnr < b->bm_bits) {
                 p_addr = bm_map_pidx(b, bm_bit_to_page_idx(b, bitnr));
-                i = generic_test_le_bit(bitnr & BPP_MASK, p_addr) ? 1 : 0;
+                i = generic_test_le_bit(bitnr & BITS_PER_PAGE_MASK, p_addr) ? 1 : 0;
                 bm_unmap(p_addr);
         } else if (bitnr == b->bm_bits) {
                 i = -1;
@@ -1517,13 +1557,15 @@ int drbd_bm_e_weight(struct drbd_conf *mdev, unsigned long enr)
         return count;
 }
 
-/* set all bits covered by the AL-extent al_enr */
+/* Set all bits covered by the AL-extent al_enr.
+ * Returns number of bits changed. */
 unsigned long drbd_bm_ALe_set_all(struct drbd_conf *mdev, unsigned long al_enr)
 {
         struct drbd_bitmap *b = mdev->bitmap;
         unsigned long *p_addr, *bm;
         unsigned long weight;
-        int count, s, e, i, do_now;
+        unsigned long s, e;
+        int count, i, do_now;
         ERR_IF(!b) return 0;
         ERR_IF(!b->bm_pages) return 0;
 
@@ -1552,7 +1594,7 @@ unsigned long drbd_bm_ALe_set_all(struct drbd_conf *mdev, unsigned long al_enr)
                 if (e == b->bm_words)
                         b->bm_set -= bm_clear_surplus(b);
         } else {
-                dev_err(DEV, "start offset (%d) too large in drbd_bm_ALe_set_all\n", s);
+                dev_err(DEV, "start offset (%lu) too large in drbd_bm_ALe_set_all\n", s);
         }
         weight = b->bm_set - weight;
         spin_unlock_irq(&b->bm_lock);