From: Yu Kuai <yukuai3@xxxxxxxxxx>
READ
While creating bitmap, all pages will be allocated and read for
llbitmap,
there won't be read afterwards
WRITE
WRITE IO is divided into logical_block_size of the page, the dirty
state
of each block is tracked independently, for example:
each page is 4k, contain 8 blocks; each block is 512 bytes contain
512 bit;
| page0 | page1 | ... | page 31 |
| |
| \-----------------------\
| |
| block0 | block1 | ... | block 8|
| |
| \-----------------\
| |
| bit0 | bit1 | ... | bit511 |
From IO path, if one bit is changed to Dirty or NeedSync, the
corresponding
subpage will be marked dirty, such block must write first before the
IO is
issued. This behaviour will affect IO performance, to reduce the
impact, if
multiple bits are changed in the same block in a short time, all
bits in
this block will be changed to Dirty/NeedSync, so that there won't be
any
overhead until daemon clears dirty bits.
Also add data structure definition and comments.
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
drivers/md/md-llbitmap.c | 571
+++++++++++++++++++++++++++++++++++++++
1 file changed, 571 insertions(+)
create mode 100644 drivers/md/md-llbitmap.c
diff --git a/drivers/md/md-llbitmap.c b/drivers/md/md-llbitmap.c
new file mode 100644
index 000000000000..1a01b6777527
--- /dev/null
+++ b/drivers/md/md-llbitmap.c
@@ -0,0 +1,571 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#ifdef CONFIG_MD_LLBITMAP
+
+#include <linux/blkdev.h>
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/timer.h>
+#include <linux/sched.h>
+#include <linux/list.h>
+#include <linux/file.h>
+#include <linux/seq_file.h>
+#include <trace/events/block.h>
+
+#include "md.h"
+#include "md-bitmap.h"
+
+/*
+ * #### Background
+ *
+ * Redundant data is used to enhance data fault tolerance, and the
storage
+ * method for redundant data vary depending on the RAID levels. And
it's
+ * important to maintain the consistency of redundant data.
+ *
+ * Bitmap is used to record which data blocks have been
synchronized and which
+ * ones need to be resynchronized or recovered. Each bit in the bitmap
+ * represents a segment of data in the array. When a bit is set, it
indicates
+ * that the multiple redundant copies of that data segment may not be
+ * consistent. Data synchronization can be performed based on the
bitmap after
+ * power failure or readding a disk. If there is no bitmap, a full
disk
+ * synchronization is required.
+ *
+ * #### Key Features
+ *
+ * - IO fastpath is lockless, if user issues lots of write IO to
the same
+ * bitmap bit in a short time, only the first write have
additional overhead
+ * to update bitmap bit, no additional overhead for the following
writes;
+ * - support only resync or recover written data, means in the
case creating
+ * new array or replacing with a new disk, there is no need to do
a full disk
+ * resync/recovery;
+ *
+ * #### Key Concept
+ *
+ * ##### State Machine
+ *
+ * Each bit is one byte, contain 6 difference state, see
llbitmap_state. And
+ * there are total 8 differenct actions, see llbitmap_action, can
change state:
+ *
+ * llbitmap state machine: transitions between states
+ *
+ * | | Startwrite | Startsync | Endsync | Abortsync|
+ * | --------- | ---------- | --------- | ------- | ------- |
+ * | Unwritten | Dirty | x | x | x |
+ * | Clean | Dirty | x | x | x |
+ * | Dirty | x | x | x | x |
+ * | NeedSync | x | Syncing | x | x |
+ * | Syncing | x | Syncing | Dirty | NeedSync |
+ *
+ * | | Reload | Daemon | Discard | Stale |
+ * | --------- | -------- | ------ | --------- | --------- |
+ * | Unwritten | x | x | x | x |
+ * | Clean | x | x | Unwritten | NeedSync |
+ * | Dirty | NeedSync | Clean | Unwritten | NeedSync |
+ * | NeedSync | x | x | Unwritten | x |
+ * | Syncing | NeedSync | x | Unwritten | NeedSync |
+ *
+ * Typical scenarios:
+ *
+ * 1) Create new array
+ * All bits will be set to Unwritten by default, if --assume-clean
is set,
+ * all bits will be set to Clean instead.
+ *
+ * 2) write data, raid1/raid10 have full copy of data, while
raid456 doesn't and
+ * rely on xor data
+ *
+ * 2.1) write new data to raid1/raid10:
+ * Unwritten --StartWrite--> Dirty
+ *
+ * 2.2) write new data to raid456:
+ * Unwritten --StartWrite--> NeedSync
+ *
+ * Because the initial recover for raid456 is skipped, the xor data
is not build
+ * yet, the bit must set to NeedSync first and after lazy initial
recover is
+ * finished, the bit will finially set to Dirty(see 5.1 and 5.4);
+ *
+ * 2.3) cover write
+ * Clean --StartWrite--> Dirty
+ *
+ * 3) daemon, if the array is not degraded:
+ * Dirty --Daemon--> Clean
+ *
+ * For degraded array, the Dirty bit will never be cleared, prevent
full disk
+ * recovery while readding a removed disk.
+ *
+ * 4) discard
+ * {Clean, Dirty, NeedSync, Syncing} --Discard--> Unwritten
+ *
+ * 5) resync and recover
+ *
+ * 5.1) common process
+ * NeedSync --Startsync--> Syncing --Endsync--> Dirty --Daemon-->
Clean
+ *
+ * 5.2) resync after power failure
+ * Dirty --Reload--> NeedSync
+ *
+ * 5.3) recover while replacing with a new disk
+ * By default, the old bitmap framework will recover all data, and
llbitmap
+ * implement this by a new helper, see llbitmap_skip_sync_blocks:
+ *
+ * skip recover for bits other than dirty or clean;
+ *
+ * 5.4) lazy initial recover for raid5:
+ * By default, the old bitmap framework will only allow new recover
when there
+ * are spares(new disk), a new recovery flag
MD_RECOVERY_LAZY_RECOVER is add
+ * to perform raid456 lazy recover for set bits(from 2.2).
+ *
+ * ##### Bitmap IO
+ *
+ * ##### Chunksize
+ *
+ * The default bitmap size is 128k, incluing 1k bitmap super block,
and
+ * the default size of segment of data in the array each
bit(chunksize) is 64k,
+ * and chunksize will adjust to twice the old size each time if the
total number
+ * bits is not less than 127k.(see llbitmap_init)
+ *
+ * ##### READ
+ *
+ * While creating bitmap, all pages will be allocated and read for
llbitmap,
+ * there won't be read afterwards
+ *
+ * ##### WRITE
+ *
+ * WRITE IO is divided into logical_block_size of the array, the
dirty state
+ * of each block is tracked independently, for example:
+ *
+ * each page is 4k, contain 8 blocks; each block is 512 bytes
contain 512 bit;
+ *
+ * | page0 | page1 | ... | page 31 |
+ * | |
+ * | \-----------------------\
+ * | |
+ * | block0 | block1 | ... | block 8|
+ * | |
+ * | \-----------------\
+ * | |
+ * | bit0 | bit1 | ... | bit511 |
+ *
+ * From IO path, if one bit is changed to Dirty or NeedSync, the
corresponding
+ * subpage will be marked dirty, such block must write first before
the IO is
+ * issued. This behaviour will affect IO performance, to reduce the
impact, if
+ * multiple bits are changed in the same block in a short time, all
bits in this
+ * block will be changed to Dirty/NeedSync, so that there won't be
any overhead
+ * until daemon clears dirty bits.
+ *
+ * ##### Dirty Bits syncronization
+ *
+ * IO fast path will set bits to dirty, and those dirty bits will
be cleared
+ * by daemon after IO is done. llbitmap_page_ctl is used to
synchronize between
+ * IO path and daemon;
+ *
+ * IO path:
+ * 1) try to grab a reference, if succeed, set expire time after
5s and return;
+ * 2) if failed to grab a reference, wait for daemon to finish
clearing dirty
+ * bits;
+ *
+ * Daemon(Daemon will be waken up every daemon_sleep seconds):
+ * For each page:
+ * 1) check if page expired, if not skip this page; for expired page:
+ * 2) suspend the page and wait for inflight write IO to be done;
+ * 3) change dirty page to clean;
+ * 4) resume the page;
+ */
+
+#define BITMAP_SB_SIZE 1024
+
+/* 64k is the max IO size of sync IO for raid1/raid10 */
+#define MIN_CHUNK_SIZE (64 * 2)
+
+/* By default, daemon will be waken up every 30s */
+#define DEFAULT_DAEMON_SLEEP 30
+
+/*
+ * Dirtied bits that have not been accessed for more than 5s will
be cleared
+ * by daemon.
+ */
+#define BARRIER_IDLE 5
+
+enum llbitmap_state {
+ /* No valid data, init state after assemble the array */
+ BitUnwritten = 0,
+ /* data is consistent */
+ BitClean,
+ /* data will be consistent after IO is done, set directly for
writes */
+ BitDirty,
+ /*
+ * data need to be resynchronized:
+ * 1) set directly for writes if array is degraded, prevent
full disk
+ * synchronization after readding a disk;
+ * 2) reassemble the array after power failure, and dirty bits are
+ * found after reloading the bitmap;
+ * 3) set for first write for raid5, to build initial xor data
lazily
+ */
+ BitNeedSync,
+ /* data is synchronizing */
+ BitSyncing,
+ nr_llbitmap_state,
+ BitNone = 0xff,
+};
+
+enum llbitmap_action {
+ /* User write new data, this is the only action from IO fast
path */
+ BitmapActionStartwrite = 0,
+ /* Start recovery */
+ BitmapActionStartsync,
+ /* Finish recovery */
+ BitmapActionEndsync,
+ /* Failed recovery */
+ BitmapActionAbortsync,
+ /* Reassemble the array */
+ BitmapActionReload,
+ /* Daemon thread is trying to clear dirty bits */
+ BitmapActionDaemon,
+ /* Data is deleted */
+ BitmapActionDiscard,
+ /*
+ * Bitmap is stale, mark all bits in addition to BitUnwritten to
+ * BitNeedSync.
+ */
+ BitmapActionStale,
+ nr_llbitmap_action,
+ /* Init state is BitUnwritten */
+ BitmapActionInit,
+};
+
+enum llbitmap_page_state {
+ LLPageFlush = 0,
+ LLPageDirty,
+};
+
+struct llbitmap_page_ctl {
+ char *state;
+ struct page *page;
+ unsigned long expire;
+ unsigned long flags;
+ wait_queue_head_t wait;
+ struct percpu_ref active;
+ /* Per block size dirty state, maximum 64k page / 1 sector =
128 */
+ unsigned long dirty[];
+};
+
+struct llbitmap {
+ struct mddev *mddev;
+ struct llbitmap_page_ctl **pctl;
+
+ unsigned int nr_pages;
+ unsigned int io_size;
+ unsigned int bits_per_page;
+
+ /* shift of one chunk */
+ unsigned long chunkshift;
+ /* size of one chunk in sector */
+ unsigned long chunksize;
+ /* total number of chunks */
+ unsigned long chunks;
+ unsigned long last_end_sync;
+ /* fires on first BitDirty state */
+ struct timer_list pending_timer;
+ struct work_struct daemon_work;
+
+ unsigned long flags;
+ __u64 events_cleared;
+
+ /* for slow disks */
+ atomic_t behind_writes;
+ wait_queue_head_t behind_wait;
+};
+
+struct llbitmap_unplug_work {
+ struct work_struct work;
+ struct llbitmap *llbitmap;
+ struct completion *done;
+};
+
+static struct workqueue_struct *md_llbitmap_io_wq;
+static struct workqueue_struct *md_llbitmap_unplug_wq;
+
+static char state_machine[nr_llbitmap_state][nr_llbitmap_action] = {
+ [BitUnwritten] = {
+ [BitmapActionStartwrite] = BitDirty,
+ [BitmapActionStartsync] = BitNone,
+ [BitmapActionEndsync] = BitNone,
+ [BitmapActionAbortsync] = BitNone,
+ [BitmapActionReload] = BitNone,
+ [BitmapActionDaemon] = BitNone,
+ [BitmapActionDiscard] = BitNone,
+ [BitmapActionStale] = BitNone,
+ },
+ [BitClean] = {
+ [BitmapActionStartwrite] = BitDirty,
+ [BitmapActionStartsync] = BitNone,
+ [BitmapActionEndsync] = BitNone,
+ [BitmapActionAbortsync] = BitNone,
+ [BitmapActionReload] = BitNone,
+ [BitmapActionDaemon] = BitNone,
+ [BitmapActionDiscard] = BitUnwritten,
+ [BitmapActionStale] = BitNeedSync,
+ },
+ [BitDirty] = {
+ [BitmapActionStartwrite] = BitNone,
+ [BitmapActionStartsync] = BitNone,
+ [BitmapActionEndsync] = BitNone,
+ [BitmapActionAbortsync] = BitNone,
+ [BitmapActionReload] = BitNeedSync,
+ [BitmapActionDaemon] = BitClean,
+ [BitmapActionDiscard] = BitUnwritten,
+ [BitmapActionStale] = BitNeedSync,
+ },
+ [BitNeedSync] = {
+ [BitmapActionStartwrite] = BitNone,
+ [BitmapActionStartsync] = BitSyncing,
+ [BitmapActionEndsync] = BitNone,
+ [BitmapActionAbortsync] = BitNone,
+ [BitmapActionReload] = BitNone,
+ [BitmapActionDaemon] = BitNone,
+ [BitmapActionDiscard] = BitUnwritten,
+ [BitmapActionStale] = BitNone,
+ },
+ [BitSyncing] = {
+ [BitmapActionStartwrite] = BitNone,
+ [BitmapActionStartsync] = BitSyncing,
+ [BitmapActionEndsync] = BitDirty,
+ [BitmapActionAbortsync] = BitNeedSync,
+ [BitmapActionReload] = BitNeedSync,
+ [BitmapActionDaemon] = BitNone,
+ [BitmapActionDiscard] = BitUnwritten,
+ [BitmapActionStale] = BitNeedSync,
+ },
+};
+
+static enum llbitmap_state llbitmap_read(struct llbitmap *llbitmap,
loff_t pos)
+{
+ unsigned int idx;
+ unsigned int offset;
+
+ pos += BITMAP_SB_SIZE;
+ idx = pos >> PAGE_SHIFT;
+ offset = offset_in_page(pos);
+
+ return llbitmap->pctl[idx]->state[offset];
+}
+
+/* set all the bits in the subpage as dirty */
+static void llbitmap_infect_dirty_bits(struct llbitmap *llbitmap,
+ struct llbitmap_page_ctl *pctl,
+ unsigned int bit, unsigned int offset)
+{
+ bool level_456 = raid_is_456(llbitmap->mddev);
+ unsigned int io_size = llbitmap->io_size;
+ int pos;
+
+ for (pos = bit * io_size; pos < (bit + 1) * io_size; pos++) {
+ if (pos == offset)
+ continue;
+
+ switch (pctl->state[pos]) {
+ case BitUnwritten:
+ pctl->state[pos] = level_456 ? BitNeedSync : BitDirty;
+ break;
+ case BitClean:
+ pctl->state[pos] = BitDirty;
+ break;
+ };
+ }
+
+}
+
+static void llbitmap_set_page_dirty(struct llbitmap *llbitmap, int
idx,
+ int offset)
+{
+ struct llbitmap_page_ctl *pctl = llbitmap->pctl[idx];
+ unsigned int io_size = llbitmap->io_size;
+ int bit = offset / io_size;
+ int pos;
+
+ if (!test_bit(LLPageDirty, &pctl->flags))
+ set_bit(LLPageDirty, &pctl->flags);
+
+ /*
+ * The subpage usually contains a total of 512 bits. If any
single bit
+ * within the subpage is marked as dirty, the entire sector
will be
+ * written. To avoid impacting write performance, when multiple
bits
+ * within the same sector are modified within a short time
frame, all
+ * bits in the sector will be collectively marked as dirty at
once.
+ */
+ if (test_and_set_bit(bit, pctl->dirty)) {
+ llbitmap_infect_dirty_bits(llbitmap, pctl, bit, offset);
+ return;
+ }
+
+ for (pos = bit * io_size; pos < (bit + 1) * io_size; pos++) {
+ if (pos == offset)
+ continue;
+ if (pctl->state[pos] == BitDirty ||
+ pctl->state[pos] == BitNeedSync) {
+ llbitmap_infect_dirty_bits(llbitmap, pctl, bit, offset);
+ return;
+ }
+ }
+}
+
+static void llbitmap_write(struct llbitmap *llbitmap, enum
llbitmap_state state,
+ loff_t pos)
+{
+ unsigned int idx;
+ unsigned int offset;
+
+ pos += BITMAP_SB_SIZE;
+ idx = pos >> PAGE_SHIFT;
+ offset = offset_in_page(pos);
+
+ llbitmap->pctl[idx]->state[offset] = state;
+ if (state == BitDirty || state == BitNeedSync)
+ llbitmap_set_page_dirty(llbitmap, idx, offset);
+}
+
+static struct page *llbitmap_read_page(struct llbitmap *llbitmap,
int idx)
+{
+ struct mddev *mddev = llbitmap->mddev;
+ struct page *page = NULL;
+ struct md_rdev *rdev;
+
+ if (llbitmap->pctl && llbitmap->pctl[idx])
+ page = llbitmap->pctl[idx]->page;
+ if (page)
+ return page;
+
+ page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+ if (!page)
+ return ERR_PTR(-ENOMEM);
+
+ rdev_for_each(rdev, mddev) {
+ sector_t sector;
+
+ if (rdev->raid_disk < 0 || test_bit(Faulty, &rdev->flags))
+ continue;
+
+ sector = mddev->bitmap_info.offset +
+ (idx << PAGE_SECTORS_SHIFT);
+
+ if (sync_page_io(rdev, sector, PAGE_SIZE, page, REQ_OP_READ,
+ true))
+ return page;
+
+ md_error(mddev, rdev);
+ }
+
+ __free_page(page);
+ return ERR_PTR(-EIO);
+}
+
+static void llbitmap_write_page(struct llbitmap *llbitmap, int idx)
+{
+ struct page *page = llbitmap->pctl[idx]->page;
+ struct mddev *mddev = llbitmap->mddev;
+ struct md_rdev *rdev;
+ int bit;
+
+ for (bit = 0; bit < llbitmap->bits_per_page; bit++) {
+ struct llbitmap_page_ctl *pctl = llbitmap->pctl[idx];
+
+ if (!test_and_clear_bit(bit, pctl->dirty))
+ continue;
+
+ rdev_for_each(rdev, mddev) {
+ sector_t sector;
+ sector_t bit_sector = llbitmap->io_size >> SECTOR_SHIFT;
+
+ if (rdev->raid_disk < 0 || test_bit(Faulty, &rdev->flags))
+ continue;
+
+ sector = mddev->bitmap_info.offset + rdev->sb_start +
+ (idx << PAGE_SECTORS_SHIFT) +
+ bit * bit_sector;
+ md_write_metadata(mddev, rdev, sector,
+ llbitmap->io_size, page,
+ bit * llbitmap->io_size);
+ }
+ }
+}
+
+static void active_release(struct percpu_ref *ref)
+{
+ struct llbitmap_page_ctl *pctl =
+ container_of(ref, struct llbitmap_page_ctl, active);
+
+ wake_up(&pctl->wait);
+}
+
+static void llbitmap_free_pages(struct llbitmap *llbitmap)
+{
+ int i;
+
+ if (!llbitmap->pctl)
+ return;
+
+ for (i = 0; i < llbitmap->nr_pages; i++) {
+ struct llbitmap_page_ctl *pctl = llbitmap->pctl[i];
+
+ if (!pctl || !pctl->page)
+ break;
+
+ __free_page(pctl->page);
+ percpu_ref_exit(&pctl->active);
+ }
+
+ kfree(llbitmap->pctl[0]);
+ kfree(llbitmap->pctl);
+ llbitmap->pctl = NULL;
+}
+
+static int llbitmap_cache_pages(struct llbitmap *llbitmap)
+{
+ struct llbitmap_page_ctl *pctl;
+ unsigned int nr_pages = DIV_ROUND_UP(llbitmap->chunks +
BITMAP_SB_SIZE,
+ PAGE_SIZE);
+ unsigned int size = struct_size(pctl, dirty,
+ BITS_TO_LONGS(llbitmap->bits_per_page));
+ int i;
+
+ llbitmap->pctl = kmalloc_array(nr_pages, sizeof(void *),
+ GFP_KERNEL | __GFP_ZERO);
+ if (!llbitmap->pctl)
+ return -ENOMEM;
+
+ size = round_up(size, cache_line_size());
+ pctl = kmalloc_array(nr_pages, size, GFP_KERNEL | __GFP_ZERO);
+ if (!pctl) {
+ kfree(llbitmap->pctl);
+ return -ENOMEM;
+ }
+
+ llbitmap->nr_pages = nr_pages;
+
+ for (i = 0; i < nr_pages; i++, pctl = (void *)pctl + size) {
+ struct page *page = llbitmap_read_page(llbitmap, i);
+
+ llbitmap->pctl[i] = pctl;
+
+ if (IS_ERR(page)) {
+ llbitmap_free_pages(llbitmap);
+ return PTR_ERR(page);
+ }
+
+ if (percpu_ref_init(&pctl->active, active_release,
+ PERCPU_REF_ALLOW_REINIT, GFP_KERNEL)) {
+ __free_page(page);
+ llbitmap_free_pages(llbitmap);
+ return -ENOMEM;
+ }
+
+ pctl->page = page;
+ pctl->state = page_address(page);
+ init_waitqueue_head(&pctl->wait);
+ }
+
+ return 0;
+}
+
+#endif /* CONFIG_MD_LLBITMAP */
