On Mon, 25 Oct 2010, Ted Ts'o wrote: > On Mon, Sep 27, 2010 at 04:09:59PM +0200, Lukas Czerner wrote: > > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c > > index 93eb6c2..80a5139 100644 > > --- a/fs/ext4/mballoc.c > > +++ b/fs/ext4/mballoc.c > .... > > + struct ext4_buddy e4b; > > + ext4_fsblk_t first_group, last_group; > > This should be ext4_group_t, shouldn't it? Right, it should be. Sorry about that. > > > + /* Determine first and last group to examine based on start and len */ > > + first_group = (start - le32_to_cpu(es->s_first_data_block)) / > > + EXT4_BLOCKS_PER_GROUP(sb); > > + last_group = (start + len - le32_to_cpu(es->s_first_data_block)) / > > + EXT4_BLOCKS_PER_GROUP(sb); > > I've tried compiling this for 32-bit x86, and this blows up because > you can't divide long long's in the kernel. (This is what do_div is > for, and it's why ext4_get_group_no_and_offset() exists.) I am ashamed, I probably should test patches on different architectures. Thanks. > > > + first_block = (start - le32_to_cpu(es->s_first_data_block)) % > > + EXT4_BLOCKS_PER_GROUP(sb); > > + last_block = EXT4_BLOCKS_PER_GROUP(sb); > > This means that the ext4 FITRIM ioctl will trim to the end of the > blockgroup, and not just to the last block specified by the user. Is > this intentional? If the group is NOT last group, or (start+len) is aligned to the EXT4_BLOCK_PER_GROUP() boundary we will trim all blocks in this particular block group. Otherwise we will know how much we need to trim in this group to satisfy user request if (len >= EXT4_BLOCKS_PER_GROUP(sb)) len -= (EXT4_BLOCKS_PER_GROUP(sb) - first_block); else last_block = len; because we do keep track of how many block we need to trim by decreasing len. > > Also, it looks like there's nothing to check for the last blockgroup, > where the last block might be less than a grpblk_t offset of > EXT4_BLOCKS_PER_GROUP()? This is not a problem, because when traversing the bitmap we will hit the end of the group anyway, because those blocks (out of filesystem) are marked as used in the bitmap and hence: start = mb_find_next_zero_bit(bitmap, max, start); if (start >= max) break; will end the traversing without any attempt to trim blocks out of filesystem boundary. > > - Ted > -Lukas -- 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
