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Commit 6c7f74f7 authored by Artem Bityutskiy's avatar Artem Bityutskiy
Browse files

UBIFS: use max_write_size for write-buffers 



Switch write-buffers from 'c->min_io_size' to 'c->max_write_size' which
presumably has to be more write speed-efficient. However, when write-buffer
is synchronized, write only the the min. I/O units which contain the
data, do not write whole write-buffer. This is more space-efficient.

Additionally, this patch takes into account that the LEB might not start
from the max. write unit-aligned address.

Signed-off-by: default avatarArtem Bityutskiy <Artem.Bityutskiy@nokia.com>
parent 3c89f396

fs/ubifs/io.c

+137 −44
Original line number Diff line number Diff line
@@ -31,6 +31,26 @@ 
 * buffer is full or when it is not used for some time (by timer). This is

 * similar to the mechanism is used by JFFS2.

 *

 * UBIFS distinguishes between minimum write size (@c->min_io_size) and maximum

 * write size (@c->max_write_size). The latter is the maximum amount of bytes

 * the underlying flash is able to program at a time, and writing in

 * @c->max_write_size units should presumably be faster. Obviously,

 * @c->min_io_size <= @c->max_write_size. Write-buffers are of

 * @c->max_write_size bytes in size for maximum performance. However, when a

 * write-buffer is flushed, only the portion of it (aligned to @c->min_io_size

 * boundary) which contains data is written, not the whole write-buffer,

 * because this is more space-efficient.

 *

 * This optimization adds few complications to the code. Indeed, on the one

 * hand, we want to write in optimal @c->max_write_size bytes chunks, which

 * also means aligning writes at the @c->max_write_size bytes offsets. On the

 * other hand, we do not want to waste space when synchronizing the write

 * buffer, so during synchronization we writes in smaller chunks. And this makes

 * the next write offset to be not aligned to @c->max_write_size bytes. So the

 * have to make sure that the write-buffer offset (@wbuf->offs) becomes aligned

 * to @c->max_write_size bytes again. We do this by temporarily shrinking

 * write-buffer size (@wbuf->size).

 *

 * Write-buffers are defined by 'struct ubifs_wbuf' objects and protected by

 * mutexes defined inside these objects. Since sometimes upper-level code

 * has to lock the write-buffer (e.g. journal space reservation code), many
@@ -46,8 +66,8 @@ 
 * UBIFS uses padding when it pads to the next min. I/O unit. In this case it

 * uses padding nodes or padding bytes, if the padding node does not fit.

 *

 * All UBIFS nodes are protected by CRC checksums and UBIFS checks all nodes

 * every time they are read from the flash media.

 * All UBIFS nodes are protected by CRC checksums and UBIFS checks CRC when

 * they are read from the flash media.

 */



#include <linux/crc32.h>
@@ -347,11 +367,17 @@ static void cancel_wbuf_timer_nolock(struct ubifs_wbuf *wbuf) 
 *

 * This function synchronizes write-buffer @buf and returns zero in case of

 * success or a negative error code in case of failure.

 *

 * Note, although write-buffers are of @c->max_write_size, this function does

 * not necessarily writes all @c->max_write_size bytes to the flash. Instead,

 * if the write-buffer is only partially filled with data, only the used part

 * of the write-buffer (aligned on @c->min_io_size boundary) is synchronized.

 * This way we waste less space.

 */

int ubifs_wbuf_sync_nolock(struct ubifs_wbuf *wbuf)

{

	struct ubifs_info *c = wbuf->c;

	int err, dirt;

	int err, dirt, sync_len;



	cancel_wbuf_timer_nolock(wbuf);

	if (!wbuf->used || wbuf->lnum == -1)
@@ -366,26 +392,48 @@ int ubifs_wbuf_sync_nolock(struct ubifs_wbuf *wbuf) 
	ubifs_assert(wbuf->size <= c->max_write_size);

	ubifs_assert(wbuf->size % c->min_io_size == 0);

	ubifs_assert(!c->ro_media && !c->ro_mount);

	if (c->leb_size - wbuf->offs >= c->max_write_size)

		ubifs_assert(!((wbuf->offs + wbuf->size) % c->max_write_size ));



	if (c->ro_error)

		return -EROFS;



	ubifs_pad(c, wbuf->buf + wbuf->used, wbuf->avail);

	/*

	 * Do not write whole write buffer but write only the minimum necessary

	 * amount of min. I/O units.

	 */

	sync_len = ALIGN(wbuf->used, c->min_io_size);

	dirt = sync_len - wbuf->used;

	if (dirt)

		ubifs_pad(c, wbuf->buf + wbuf->used, dirt);

	err = ubi_leb_write(c->ubi, wbuf->lnum, wbuf->buf, wbuf->offs,

			    wbuf->size, wbuf->dtype);

			    sync_len, wbuf->dtype);

	if (err) {

		ubifs_err("cannot write %d bytes to LEB %d:%d",

			  wbuf->size, wbuf->lnum, wbuf->offs);

			  sync_len, wbuf->lnum, wbuf->offs);

		dbg_dump_stack();

		return err;

	}



	dirt = wbuf->avail;



	spin_lock(&wbuf->lock);

	wbuf->offs += wbuf->size;

	wbuf->avail = c->min_io_size;

	wbuf->size = c->min_io_size;

	wbuf->offs += sync_len;

	/*

	 * Now @wbuf->offs is not necessarily aligned to @c->max_write_size.

	 * But our goal is to optimize writes and make sure we write in

	 * @c->max_write_size chunks and to @c->max_write_size-aligned offset.

	 * Thus, if @wbuf->offs is not aligned to @c->max_write_size now, make

	 * sure that @wbuf->offs + @wbuf->size is aligned to

	 * @c->max_write_size. This way we make sure that after next

	 * write-buffer flush we are again at the optimal offset (aligned to

	 * @c->max_write_size).

	 */

	if (c->leb_size - wbuf->offs < c->max_write_size)

		wbuf->size = c->leb_size - wbuf->offs;

	else if (wbuf->offs & (c->max_write_size - 1))

		wbuf->size = ALIGN(wbuf->offs, c->max_write_size) - wbuf->offs;

	else

		wbuf->size = c->max_write_size;

	wbuf->avail = wbuf->size;

	wbuf->used = 0;

	wbuf->next_ino = 0;

	spin_unlock(&wbuf->lock);
@@ -428,8 +476,13 @@ int ubifs_wbuf_seek_nolock(struct ubifs_wbuf *wbuf, int lnum, int offs, 
	spin_lock(&wbuf->lock);

	wbuf->lnum = lnum;

	wbuf->offs = offs;

	wbuf->avail = c->min_io_size;

	wbuf->size = c->min_io_size;

	if (c->leb_size - wbuf->offs < c->max_write_size)

		wbuf->size = c->leb_size - wbuf->offs;

	else if (wbuf->offs & (c->max_write_size - 1))

		wbuf->size = ALIGN(wbuf->offs, c->max_write_size) - wbuf->offs;

	else

		wbuf->size = c->max_write_size;

	wbuf->avail = wbuf->size;

	wbuf->used = 0;

	spin_unlock(&wbuf->lock);

	wbuf->dtype = dtype;
@@ -509,8 +562,9 @@ int ubifs_bg_wbufs_sync(struct ubifs_info *c) 
 *

 * This function writes data to flash via write-buffer @wbuf. This means that

 * the last piece of the node won't reach the flash media immediately if it

 * does not take whole minimal I/O unit. Instead, the node will sit in RAM

 * until the write-buffer is synchronized (e.g., by timer).

 * does not take whole max. write unit (@c->max_write_size). Instead, the node

 * will sit in RAM until the write-buffer is synchronized (e.g., by timer, or

 * because more data are appended to the write-buffer).

 *

 * This function returns zero in case of success and a negative error code in

 * case of failure. If the node cannot be written because there is no more
@@ -533,6 +587,8 @@ int ubifs_wbuf_write_nolock(struct ubifs_wbuf *wbuf, void *buf, int len) 
	ubifs_assert(wbuf->size % c->min_io_size == 0);

	ubifs_assert(mutex_is_locked(&wbuf->io_mutex));

	ubifs_assert(!c->ro_media && !c->ro_mount);

	if (c->leb_size - wbuf->offs >= c->max_write_size)

		ubifs_assert(!((wbuf->offs + wbuf->size) % c->max_write_size ));



	if (c->leb_size - wbuf->offs - wbuf->used < aligned_len) {

		err = -ENOSPC;
@@ -561,9 +617,12 @@ int ubifs_wbuf_write_nolock(struct ubifs_wbuf *wbuf, void *buf, int len) 
				goto out;



			spin_lock(&wbuf->lock);

			wbuf->offs += c->min_io_size;

			wbuf->avail = c->min_io_size;

			wbuf->size = c->min_io_size;

			wbuf->offs += wbuf->size;

			if (c->leb_size - wbuf->offs >= c->max_write_size)

				wbuf->size = c->max_write_size;

			else

				wbuf->size = c->leb_size - wbuf->offs;

			wbuf->avail = wbuf->size;

			wbuf->used = 0;

			wbuf->next_ino = 0;

			spin_unlock(&wbuf->lock);
@@ -577,10 +636,14 @@ int ubifs_wbuf_write_nolock(struct ubifs_wbuf *wbuf, void *buf, int len) 
		goto exit;

	}



	offs = wbuf->offs;

	written = 0;



	if (wbuf->used) {

		/*

	 * The node is large enough and does not fit entirely within current

	 * minimal I/O unit. We have to fill and flush write-buffer and switch

	 * to the next min. I/O unit.

		 * The node is large enough and does not fit entirely within

		 * current available space. We have to fill and flush

		 * write-buffer and switch to the next max. write unit.

		 */

		dbg_io("flush jhead %s wbuf to LEB %d:%d",

		       dbg_jhead(wbuf->jhead), wbuf->lnum, wbuf->offs);
@@ -590,20 +653,40 @@ int ubifs_wbuf_write_nolock(struct ubifs_wbuf *wbuf, void *buf, int len) 
		if (err)

			goto out;



	offs = wbuf->offs + wbuf->size;

		offs += wbuf->size;

		len -= wbuf->avail;

		aligned_len -= wbuf->avail;

	written = wbuf->avail;

		written += wbuf->avail;

	} else if (wbuf->offs & (c->max_write_size - 1)) {

		/*

		 * The write-buffer offset is not aligned to

		 * @c->max_write_size and @wbuf->size is less than

		 * @c->max_write_size. Write @wbuf->size bytes to make sure the

		 * following writes are done in optimal @c->max_write_size

		 * chunks.

		 */

		dbg_io("write %d bytes to LEB %d:%d",

		       wbuf->size, wbuf->lnum, wbuf->offs);

		err = ubi_leb_write(c->ubi, wbuf->lnum, buf, wbuf->offs,

				    wbuf->size, wbuf->dtype);

		if (err)

			goto out;



		offs += wbuf->size;

		len -= wbuf->size;

		aligned_len -= wbuf->size;

		written += wbuf->size;

	}



	/*

	 * The remaining data may take more whole min. I/O units, so write the

	 * remains multiple to min. I/O unit size directly to the flash media.

	 * The remaining data may take more whole max. write units, so write the

	 * remains multiple to max. write unit size directly to the flash media.

	 * We align node length to 8-byte boundary because we anyway flash wbuf

	 * if the remaining space is less than 8 bytes.

	 */

	n = aligned_len >> c->min_io_shift;

	n = aligned_len >> c->max_write_shift;

	if (n) {

		n <<= c->min_io_shift;

		n <<= c->max_write_shift;

		dbg_io("write %d bytes to LEB %d:%d", n, wbuf->lnum, offs);

		err = ubi_leb_write(c->ubi, wbuf->lnum, buf + written, offs, n,

				    wbuf->dtype);
@@ -619,15 +702,18 @@ int ubifs_wbuf_write_nolock(struct ubifs_wbuf *wbuf, void *buf, int len) 
	if (aligned_len)

		/*

		 * And now we have what's left and what does not take whole

		 * min. I/O unit, so write it to the write-buffer and we are

		 * max. write unit, so write it to the write-buffer and we are

		 * done.

		 */

		memcpy(wbuf->buf, buf + written, len);



	wbuf->offs = offs;

	if (c->leb_size - wbuf->offs >= c->max_write_size)

		wbuf->size = c->max_write_size;

	else

		wbuf->size = c->leb_size - wbuf->offs;

	wbuf->avail = wbuf->size - aligned_len;

	wbuf->used = aligned_len;

	wbuf->avail = c->min_io_size - aligned_len;

	wbuf->size = c->min_io_size;

	wbuf->next_ino = 0;

	spin_unlock(&wbuf->lock);
@@ -851,11 +937,11 @@ int ubifs_wbuf_init(struct ubifs_info *c, struct ubifs_wbuf *wbuf) 
{

	size_t size;



	wbuf->buf = kmalloc(c->min_io_size, GFP_KERNEL);

	wbuf->buf = kmalloc(c->max_write_size, GFP_KERNEL);

	if (!wbuf->buf)

		return -ENOMEM;



	size = (c->min_io_size / UBIFS_CH_SZ + 1) * sizeof(ino_t);

	size = (c->max_write_size / UBIFS_CH_SZ + 1) * sizeof(ino_t);

	wbuf->inodes = kmalloc(size, GFP_KERNEL);

	if (!wbuf->inodes) {

		kfree(wbuf->buf);
@@ -865,7 +951,14 @@ int ubifs_wbuf_init(struct ubifs_info *c, struct ubifs_wbuf *wbuf) 


	wbuf->used = 0;

	wbuf->lnum = wbuf->offs = -1;

	wbuf->avail = wbuf->size = c->min_io_size;

	/*

	 * If the LEB starts at the max. write size aligned address, then

	 * write-buffer size has to be set to @c->max_write_size. Otherwise,

	 * set it to something smaller so that it ends at the closest max.

	 * write size boundary.

	 */

	size = c->max_write_size - (c->leb_start % c->max_write_size);

	wbuf->avail = wbuf->size = size;

	wbuf->dtype = UBI_UNKNOWN;

	wbuf->sync_callback = NULL;

	mutex_init(&wbuf->io_mutex);