Messages in this thread Patch in this message | | | Date | Sun, 19 May 2002 12:43:36 -0700 | From | Andrew Morton <> | Subject | [patch 11/15] ext2: preread inode backing blocks |
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When ext2 creates a new inode, perform an asynchronous preread against its backing block.
Without this patch, many-file writeout gets stalled by having to read many individual inode table blocks in the middle of writeback.
It's worth about a 20% gain in writeback bandwidth for the many-file writeback case.
ext3 already reads the inode's backing block in ext3_new_inode->ext3_mark_inode_dirty, so no change is needed there.
A backport to 2.4 would make sense.
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--- 2.5.16/fs/ext2/ialloc.c~tuning-20-ext2-preread-inode Sun May 19 11:49:49 2002 +++ 2.5.16-akpm/fs/ext2/ialloc.c Sun May 19 11:49:49 2002 @@ -218,6 +218,44 @@ error_return: } /* + * We perform asynchronous prereading of the new inode's inode block when + * we create the inode, in the expectation that the inode will be written + * back soon. There are two reasons: + * + * - When creating a large number of files, the async prereads will be + * nicely merged into large reads + * - When writing out a large number of inodes, we don't need to keep on + * stalling the writes while we read the inode block. + * + * FIXME: ext2_get_group_desc() needs to be simplified. + */ +static void ext2_preread_inode(struct inode *inode) +{ + unsigned long block_group; + unsigned long offset; + unsigned long block; + struct buffer_head *bh; + struct ext2_group_desc * gdp; + + block_group = (inode->i_ino - 1) / EXT2_INODES_PER_GROUP(inode->i_sb); + gdp = ext2_get_group_desc(inode->i_sb, block_group, &bh); + if (gdp == NULL) + return; + + /* + * Figure out the offset within the block group inode table + */ + offset = ((inode->i_ino - 1) % EXT2_INODES_PER_GROUP(inode->i_sb)) * + EXT2_INODE_SIZE(inode->i_sb); + block = le32_to_cpu(gdp->bg_inode_table) + + (offset >> EXT2_BLOCK_SIZE_BITS(inode->i_sb)); + bh = sb_getblk(inode->i_sb, block); + if (!buffer_uptodate(bh) && !buffer_locked(bh)) + ll_rw_block(READA, 1, &bh); + __brelse(bh); +} + +/* * There are two policies for allocating an inode. If the new inode is * a directory, then a forward search is made for a block group with both * free space and a low directory-to-inode ratio; if that fails, then of @@ -417,6 +455,7 @@ repeat: return ERR_PTR(-EDQUOT); } ext2_debug ("allocating inode %lu\n", inode->i_ino); + ext2_preread_inode(inode); return inode; fail2:
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