From: Theodore Ts'o Date: Mon, 23 Feb 2009 11:46:01 +0000 (-0500) Subject: ext4: Save stack space by removing fake buffer heads X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=8dc207c0e7a259e7122ddfaf56b8bbbc3c92d685;p=linux-beck.git 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" --- diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 924ba8afc227..008b28a859d0 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -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 { @@ -2222,8 +2216,10 @@ 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))) { @@ -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;