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Date: Tue, 24 Feb 2009 00:05:48 -0500
From: Theodore Ts'o <tytso@....edu>
To: linux-ext4@...r.kernel.org
Cc: aneesh.kumar@...ux.vnet.ibm.com, Theodore Ts'o <tytso@....edu>
Subject: [PATCH, RFC] 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: "Theodore Ts'o" <tytso@....edu>
---
fs/ext4/inode.c | 83 ++++++++++++++++++++++++++-----------------------------
1 files changed, 39 insertions(+), 44 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index a533314..407aa85 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1673,7 +1673,9 @@ 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;
@@ -1707,7 +1709,7 @@ 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;
@@ -1945,7 +1947,7 @@ 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.
*
@@ -1954,18 +1956,18 @@ 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
@@ -2001,7 +2003,7 @@ 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) {
@@ -2009,7 +2011,7 @@ 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);
@@ -2021,7 +2023,8 @@ 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;
@@ -2040,12 +2043,11 @@ 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)) {
@@ -2072,19 +2074,19 @@ 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;
}
@@ -2113,7 +2115,7 @@ 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) {
@@ -2155,9 +2157,9 @@ 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;
@@ -2165,16 +2167,8 @@ 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 {
@@ -2192,8 +2186,10 @@ static int __mpage_da_writepage(struct page *page,
* with the page in ext4_da_writepage
*/
if (buffer_dirty(bh) &&
- (!buffer_mapped(bh) || buffer_delay(bh))) {
- mpage_add_bh_to_extent(mpd, logical, bh);
+ (!buffer_mapped(bh) || buffer_delay(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))) {
@@ -2205,9 +2201,8 @@ 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);
@@ -2233,9 +2228,9 @@ 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;
--
1.5.6.3
--
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