On Nov 14, 2008 11:17 +0200, Pekka J Enberg wrote: > As spotted by kmemtrace, struct ext2_sb_info is 17024 bytes and ext3_sb_info is > 17152 bytes on 64-bit which makes them a very bad fit for SLAB allocators. In > fact, both allocations are round up to the next available page size of > order 3 which is 32 KB. > > The culprit if the wasted memory is the ->s_blockgroup_lock which can be as > big as 16 KB when CONFIG_NR_CPUS is set to 32. As struct blockgroup_lock is a > perfect fit for order 2 page in the worst case, allocate ->s_blockgroup_lock > separately to avoid wasting space. > > The change shrinks struct ext2_sb_info to 592 bytes and struct ext3_sb_info to > 640 bytes which fits into a 1024 byte slab cache so now we allocate 16 KB + 1 > KB instead of 32 KB saving 15 KB of memory! > > Signed-off-by: Pekka Enberg <penberg@xxxxxxxxxxxxxx> This looks very reasonable, with some minor comments below. Could you please also include a patch for ext4. Also, Andrew prefers that the patches for ext2/ext3/ext4 are in separate emails. > --- a/include/linux/blockgroup_lock.h > +++ b/include/linux/blockgroup_lock.h > #define sb_bgl_lock(sb, block_group) \ > - (&(sb)->s_blockgroup_lock.locks[(block_group) & (NR_BG_LOCKS-1)].lock) > + (&(sb)->s_blockgroup_lock->locks[(block_group) & (NR_BG_LOCKS-1)].lock) How the struct is allocated seems like an implementation detail that doesn't belong in blockgroup_lock.h at all, because "sb" is not "struct superblock" but rather "struct ext[23]_sb_info". In fact, changing this without also patching ext4 would cause ext4 to break. I would suggest to change this to take the s_blockgroup_lock as a parameter, #define bgl_lock_ptr(bgl, block_group) (bgl->locks[(block_group) & (NR_BG_LOCKS - 1)].lock) and then in ext[234]_fs_sb.h add a new helper in the same (first) patch: #define sb_bgl_lock(sbi, block_group) bgl_lock_ptr(&sbi->s_blockgroup_lock, block_group) and remove sb_bgl_lock() from blockgroup_lock.h entirely. As part of the later patches to change the s_blockgroup_lock allocations for each of ext[234] this changes in ext[234]_fs_sb.h to: #define sb_bgl_lock(sbi, block_group) bgl_lock_ptr(sbi->s_blockgroup_lock, block_group) This allows each of the later patches to be landed separately without breaking the build. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
