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Commit 8dc207c0 authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

ext4: Save stack space by removing fake buffer heads 



Struct mpage_da_data and mpage_add_bh_to_extent() use a fake struct
buffer_head which is 104 bytes on an x86_64 system, but only use 24
bytes of the structure.  On systems that use a spinlock for atomic_t,
the stack savings will be even greater.

It turns out that using a fake struct buffer_head doesn't even save
that much code, and it makes the code more confusing since it's not
used as a "real" buffer head.  So just store pass b_size and b_state
in mpage_add_bh_to_extent(), and store b_size, b_state, and b_block_nr
in the mpage_da_data structure.

Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent ed5bde0b

fs/ext4/inode.c

+39 −44
Original line number Diff line number Diff line
@@ -1703,7 +1703,9 @@ static void ext4_da_page_release_reservation(struct page *page, 


struct mpage_da_data {

	struct inode *inode;

	struct buffer_head lbh;			/* extent of blocks */

	sector_t b_blocknr;		/* start block number of extent */

	size_t b_size;			/* size of extent */

	unsigned long b_state;		/* state of the extent */

	unsigned long first_page, next_page;	/* extent of pages */

	struct writeback_control *wbc;

	int io_done;
@@ -1737,7 +1739,7 @@ static int mpage_da_submit_io(struct mpage_da_data *mpd) 
	/*

	 * We need to start from the first_page to the next_page - 1

	 * to make sure we also write the mapped dirty buffer_heads.

	 * If we look at mpd->lbh.b_blocknr we would only be looking

	 * If we look at mpd->b_blocknr we would only be looking

	 * at the currently mapped buffer_heads.

	 */

	index = mpd->first_page;
@@ -1975,7 +1977,7 @@ static int ext4_da_get_block_write(struct inode *inode, sector_t iblock, 
/*

 * mpage_da_map_blocks - go through given space

 *

 * @mpd->lbh - bh describing space

 * @mpd - bh describing space

 *

 * The function skips space we know is already mapped to disk blocks.

 *
@@ -1984,18 +1986,18 @@ static int mpage_da_map_blocks(struct mpage_da_data *mpd) 
{

	int err = 0;

	struct buffer_head new;

	struct buffer_head *lbh = &mpd->lbh;

	sector_t next;



	/*

	 * We consider only non-mapped and non-allocated blocks

	 */

	if (buffer_mapped(lbh) && !buffer_delay(lbh))

	if ((mpd->b_state  & (1 << BH_Mapped)) &&

	    !(mpd->b_state & (1 << BH_Delay)))

		return 0;

	new.b_state = lbh->b_state;

	new.b_state = mpd->b_state;

	new.b_blocknr = 0;

	new.b_size = lbh->b_size;

	next = lbh->b_blocknr;

	new.b_size = mpd->b_size;

	next = mpd->b_blocknr;

	/*

	 * If we didn't accumulate anything

	 * to write simply return
@@ -2031,7 +2033,7 @@ static int mpage_da_map_blocks(struct mpage_da_data *mpd) 
				  "%zd with error %d\n",

				  __func__, mpd->inode->i_ino,

				  (unsigned long long)next,

				  lbh->b_size >> mpd->inode->i_blkbits, err);

				  mpd->b_size >> mpd->inode->i_blkbits, err);

		printk(KERN_EMERG "This should not happen.!! "

					"Data will be lost\n");

		if (err == -ENOSPC) {
@@ -2039,7 +2041,7 @@ static int mpage_da_map_blocks(struct mpage_da_data *mpd) 
		}

		/* invlaidate all the pages */

		ext4_da_block_invalidatepages(mpd, next,

				lbh->b_size >> mpd->inode->i_blkbits);

				mpd->b_size >> mpd->inode->i_blkbits);

		return err;

	}

	BUG_ON(new.b_size == 0);
@@ -2051,7 +2053,8 @@ static int mpage_da_map_blocks(struct mpage_da_data *mpd) 
	 * If blocks are delayed marked, we need to

	 * put actual blocknr and drop delayed bit

	 */

	if (buffer_delay(lbh) || buffer_unwritten(lbh))

	if ((mpd->b_state & (1 << BH_Delay)) ||

	    (mpd->b_state & (1 << BH_Unwritten)))

		mpage_put_bnr_to_bhs(mpd, next, &new);



	return 0;
@@ -2070,12 +2073,11 @@ static int mpage_da_map_blocks(struct mpage_da_data *mpd) 
 * the function is used to collect contig. blocks in same state

 */

static void mpage_add_bh_to_extent(struct mpage_da_data *mpd,

				   sector_t logical, struct buffer_head *bh)

				   sector_t logical, size_t b_size,

				   unsigned long b_state)

{

	sector_t next;

	size_t b_size = bh->b_size;

	struct buffer_head *lbh = &mpd->lbh;

	int nrblocks = lbh->b_size >> mpd->inode->i_blkbits;

	int nrblocks = mpd->b_size >> mpd->inode->i_blkbits;



	/* check if thereserved journal credits might overflow */

	if (!(EXT4_I(mpd->inode)->i_flags & EXT4_EXTENTS_FL)) {
@@ -2102,19 +2104,19 @@ static void mpage_add_bh_to_extent(struct mpage_da_data *mpd, 
	/*

	 * First block in the extent

	 */

	if (lbh->b_size == 0) {

		lbh->b_blocknr = logical;

		lbh->b_size = b_size;

		lbh->b_state = bh->b_state & BH_FLAGS;

	if (mpd->b_size == 0) {

		mpd->b_blocknr = logical;

		mpd->b_size = b_size;

		mpd->b_state = b_state & BH_FLAGS;

		return;

	}



	next = lbh->b_blocknr + nrblocks;

	next = mpd->b_blocknr + nrblocks;

	/*

	 * Can we merge the block to our big extent?

	 */

	if (logical == next && (bh->b_state & BH_FLAGS) == lbh->b_state) {

		lbh->b_size += b_size;

	if (logical == next && (b_state & BH_FLAGS) == mpd->b_state) {

		mpd->b_size += b_size;

		return;

	}
@@ -2143,7 +2145,7 @@ static int __mpage_da_writepage(struct page *page, 
{

	struct mpage_da_data *mpd = data;

	struct inode *inode = mpd->inode;

	struct buffer_head *bh, *head, fake;

	struct buffer_head *bh, *head;

	sector_t logical;



	if (mpd->io_done) {
@@ -2185,9 +2187,9 @@ static int __mpage_da_writepage(struct page *page, 
		/*

		 * ... and blocks

		 */

		mpd->lbh.b_size = 0;

		mpd->lbh.b_state = 0;

		mpd->lbh.b_blocknr = 0;

		mpd->b_size = 0;

		mpd->b_state = 0;

		mpd->b_blocknr = 0;

	}



	mpd->next_page = page->index + 1;
@@ -2195,16 +2197,8 @@ static int __mpage_da_writepage(struct page *page, 
		  (PAGE_CACHE_SHIFT - inode->i_blkbits);



	if (!page_has_buffers(page)) {

		/*

		 * There is no attached buffer heads yet (mmap?)

		 * we treat the page asfull of dirty blocks

		 */

		bh = &fake;

		bh->b_size = PAGE_CACHE_SIZE;

		bh->b_state = 0;

		set_buffer_dirty(bh);

		set_buffer_uptodate(bh);

		mpage_add_bh_to_extent(mpd, logical, bh);

		mpage_add_bh_to_extent(mpd, logical, PAGE_CACHE_SIZE,

				       (1 << BH_Dirty) | (1 << BH_Uptodate));

		if (mpd->io_done)

			return MPAGE_DA_EXTENT_TAIL;

	} else {
@@ -2223,7 +2217,9 @@ static int __mpage_da_writepage(struct page *page, 
			 */

			if (buffer_dirty(bh) &&

			    (!buffer_mapped(bh) || buffer_delay(bh))) {

				mpage_add_bh_to_extent(mpd, logical, bh);

				mpage_add_bh_to_extent(mpd, logical,

						       bh->b_size,

						       bh->b_state);

				if (mpd->io_done)

					return MPAGE_DA_EXTENT_TAIL;

			} else if (buffer_dirty(bh) && (buffer_mapped(bh))) {
@@ -2235,9 +2231,8 @@ static int __mpage_da_writepage(struct page *page, 
				 * unmapped buffer_head later we need to

				 * use the b_state flag of that buffer_head.

				 */

				if (mpd->lbh.b_size == 0)

					mpd->lbh.b_state =

						bh->b_state & BH_FLAGS;

				if (mpd->b_size == 0)

					mpd->b_state = bh->b_state & BH_FLAGS;

			}

			logical++;

		} while ((bh = bh->b_this_page) != head);
@@ -2263,9 +2258,9 @@ static int mpage_da_writepages(struct address_space *mapping, 
{

	int ret;



	mpd->lbh.b_size = 0;

	mpd->lbh.b_state = 0;

	mpd->lbh.b_blocknr = 0;

	mpd->b_size = 0;

	mpd->b_state = 0;

	mpd->b_blocknr = 0;

	mpd->first_page = 0;

	mpd->next_page = 0;

	mpd->io_done = 0;