From: Yongqiang Yang Subject: Re: [PATCH v2 2/3] ext4:Add two functions splitting an extent. Date: Fri, 13 May 2011 10:25:25 +0800 Message-ID: References: <1304388301-9452-1-git-send-email-xiaoqiangnk@gmail.com> <1304388301-9452-3-git-send-email-xiaoqiangnk@gmail.com> <1305235906.9708.81.camel@mingming-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, achender@linux.vnet.ibm.com To: Mingming Cao Return-path: Received: from mail-vx0-f174.google.com ([209.85.220.174]:48627 "EHLO mail-vx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751366Ab1EMCZ0 convert rfc822-to-8bit (ORCPT ); Thu, 12 May 2011 22:25:26 -0400 Received: by vxi39 with SMTP id 39so1561510vxi.19 for ; Thu, 12 May 2011 19:25:25 -0700 (PDT) In-Reply-To: <1305235906.9708.81.camel@mingming-laptop> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, May 13, 2011 at 5:31 AM, Mingming Cao wrote: > On Mon, 2011-05-02 at 19:05 -0700, Yongqiang Yang wrote: >> v0 -> v1: >> =A0 =A0-- coding style >> =A0 =A0-- try to merge extents in zeroout case too. >> >> 1] Add a function named ext4_split_extent_at() which splits an exten= t >> =A0 =A0into two extents at given logical block. >> >> 2] Add a function called ext4_split_extent() which splits an extent >> =A0 =A0into three extents. >> >> Signed-off-by: Yongqiang Yang >> Tested-by: Allison Henderson >> --- >> =A0fs/ext4/extents.c | =A0187 ++++++++++++++++++++++++++++++++++++++= +++++++++++++++ >> =A01 files changed, 187 insertions(+), 0 deletions(-) >> >> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c >> index 11f30d2..db1d67c 100644 >> --- a/fs/ext4/extents.c >> +++ b/fs/ext4/extents.c >> @@ -2554,6 +2554,193 @@ static int ext4_ext_zeroout(struct inode *in= ode, struct ext4_extent *ex) >> =A0 =A0 =A0 return ret; >> =A0} >> >> +/* >> + * used by extent splitting. >> + */ >> +#define EXT4_EXT_MAY_ZEROOUT 0x1 =A0/* safe to zeroout if split fai= ls \ >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= =A0 due to ENOSPC */ >> +#define EXT4_EXT_MARK_UNINIT1 =A0 =A0 =A0 =A00x2 =A0/* mark first h= alf uninitialized */ >> +#define EXT4_EXT_MARK_UNINIT2 =A0 =A0 =A0 =A00x4 =A0/* mark second = half uninitialized */ >> + >> +/* >> + * ext4_split_extent_at() splits an extent at given block. >> + * >> + * @handle: the journal handle >> + * @inode: the file inode >> + * @path: the path to the extent >> + * @split: the logical block where the extent is splitted. >> + * @split_flags: indicates if the extent could be zeroout if split = fails, and >> + * =A0 =A0 =A0 =A0 =A0 =A0the states(init or uninit) of new extents= =2E >> + * @flags: flags used to insert new extent to extent tree. >> + * >> + * >> + * Splits extent [a, b] into two extents [a, @split) and [@split, b= ], states >> + * of which are deterimined by split_flag. >> + * >> + * There are two cases: >> + * =A0a> the extent are splitted into two extent. >> + * =A0b> split is not needed, and just mark the extent. >> + * >> + * return 0 on success. >> + */ >> +static int ext4_split_extent_at(handle_t *handle, >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0struct inode *i= node, >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0struct ext4_ext= _path *path, >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0ext4_lblk_t spl= it, >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0int split_flag, >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0int flags) >> +{ >> + =A0 =A0 ext4_fsblk_t newblock; >> + =A0 =A0 ext4_lblk_t ee_block; >> + =A0 =A0 struct ext4_extent *ex, newex, orig_ex; >> + =A0 =A0 struct ext4_extent *ex2 =3D NULL; >> + =A0 =A0 unsigned int ee_len, depth; >> + =A0 =A0 int err =3D 0; >> + >> + =A0 =A0 ext_debug("ext4_split_extents_at: inode %lu, logical" >> + =A0 =A0 =A0 =A0 =A0 =A0 "block %llu\n", inode->i_ino, (unsigned lo= ng long)split); >> + >> + =A0 =A0 ext4_ext_show_leaf(inode, path); >> + >> + =A0 =A0 depth =3D ext_depth(inode); >> + =A0 =A0 ex =3D path[depth].p_ext; >> + =A0 =A0 ee_block =3D le32_to_cpu(ex->ee_block); >> + =A0 =A0 ee_len =3D ext4_ext_get_actual_len(ex); >> + =A0 =A0 newblock =3D split - ee_block + ext4_ext_pblock(ex); >> + >> + =A0 =A0 BUG_ON(split < ee_block || split >=3D (ee_block + ee_len))= ; >> + >> + =A0 =A0 err =3D ext4_ext_get_access(handle, inode, path + depth); >> + =A0 =A0 if (err) >> + =A0 =A0 =A0 =A0 =A0 =A0 goto out; >> + >> + =A0 =A0 if (split =3D=3D ee_block) { >> + =A0 =A0 =A0 =A0 =A0 =A0 /* >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0* case b: block @split is the block tha= t the extent begins with >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0* then we just change the state of the = extent, and splitting >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0* is not needed. >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0*/ >> + =A0 =A0 =A0 =A0 =A0 =A0 if (split_flag & EXT4_EXT_MARK_UNINIT2) >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ext4_ext_mark_uninitialize= d(ex); >> + =A0 =A0 =A0 =A0 =A0 =A0 else >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ext4_ext_mark_initialized(= ex); >> + >> + =A0 =A0 =A0 =A0 =A0 =A0 if (!(flags & EXT4_GET_BLOCKS_PRE_IO)) >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ext4_ext_try_to_merge(inod= e, path, ex); >> + >> + =A0 =A0 =A0 =A0 =A0 =A0 err =3D ext4_ext_dirty(handle, inode, path= + depth); >> + =A0 =A0 =A0 =A0 =A0 =A0 goto out; >> + =A0 =A0 } >> + >> + =A0 =A0 /* case a */ >> + =A0 =A0 memcpy(&orig_ex, ex, sizeof(orig_ex)); >> + =A0 =A0 ex->ee_len =3D cpu_to_le16(split - ee_block); >> + =A0 =A0 if (split_flag & EXT4_EXT_MARK_UNINIT1) >> + =A0 =A0 =A0 =A0 =A0 =A0 ext4_ext_mark_uninitialized(ex); >> + >> + =A0 =A0 /* >> + =A0 =A0 =A0* path may lead to new leaf, not to original leaf any m= ore >> + =A0 =A0 =A0* after ext4_ext_insert_extent() returns, >> + =A0 =A0 =A0*/ >> + =A0 =A0 err =3D ext4_ext_dirty(handle, inode, path + depth); >> + =A0 =A0 if (err) >> + =A0 =A0 =A0 =A0 =A0 =A0 goto fix_extent_len; >> + >> + =A0 =A0 ex2 =3D &newex; >> + =A0 =A0 ex2->ee_block =3D cpu_to_le32(split); >> + =A0 =A0 ex2->ee_len =A0 =3D cpu_to_le16(ee_len - (split - ee_block= )); >> + =A0 =A0 ext4_ext_store_pblock(ex2, newblock); >> + =A0 =A0 if (split_flag & EXT4_EXT_MARK_UNINIT2) >> + =A0 =A0 =A0 =A0 =A0 =A0 ext4_ext_mark_uninitialized(ex2); >> + >> + =A0 =A0 err =3D ext4_ext_insert_extent(handle, inode, path, &newex= , flags); >> + =A0 =A0 if (err =3D=3D -ENOSPC && (EXT4_EXT_MAY_ZEROOUT & split_fl= ag)) { >> + =A0 =A0 =A0 =A0 =A0 =A0 err =3D ext4_ext_zeroout(inode, &orig_ex); >> + =A0 =A0 =A0 =A0 =A0 =A0 if (err) >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto fix_extent_len; >> + =A0 =A0 =A0 =A0 =A0 =A0 /* update the extent length and mark as in= itialized */ >> + =A0 =A0 =A0 =A0 =A0 =A0 ex->ee_len =3D cpu_to_le32(ee_len); >> + =A0 =A0 =A0 =A0 =A0 =A0 ext4_ext_try_to_merge(inode, path, ex); >> + =A0 =A0 =A0 =A0 =A0 =A0 err =3D ext4_ext_dirty(handle, inode, path= + depth); >> + =A0 =A0 =A0 =A0 =A0 =A0 goto out; >> + =A0 =A0 } else if (err) >> + =A0 =A0 =A0 =A0 =A0 =A0 goto fix_extent_len; >> + >> +out: >> + =A0 =A0 ext4_ext_show_leaf(inode, path); >> + =A0 =A0 return err; >> + >> +fix_extent_len: >> + =A0 =A0 ex->ee_len =3D orig_ex.ee_len; >> + =A0 =A0 ext4_ext_dirty(handle, inode, path + depth); >> + =A0 =A0 return err; >> +} >> + >> +/* >> + * ext4_split_extents() splits an extent and mark extent which is c= overed >> + * by @map as split_flags indicates >> + * >> + * It may result in splitting the extent into multiple extents (upt= o three) >> + * There are three possibilities: >> + * =A0 a> There is no split required >> + * =A0 b> Splits in two extents: Split is happening at either end o= f the extent >> + * =A0 c> Splits in three extents: Somone is splitting in middle of= the extent >> + * >> + */ >> +static int ext4_split_extent(handle_t *handle, >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 struct inode *= inode, >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 struct ext4_ex= t_path *path, >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 struct ext4_ma= p_blocks *map, >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 int split_flag= , >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 int flags) >> +{ >> + =A0 =A0 ext4_lblk_t ee_block; >> + =A0 =A0 struct ext4_extent *ex; >> + =A0 =A0 unsigned int ee_len, depth; >> + =A0 =A0 int err =3D 0; >> + =A0 =A0 int uninitialized; >> + =A0 =A0 int split_flag1, flags1; >> + >> + =A0 =A0 depth =3D ext_depth(inode); >> + =A0 =A0 ex =3D path[depth].p_ext; >> + =A0 =A0 ee_block =3D le32_to_cpu(ex->ee_block); >> + =A0 =A0 ee_len =3D ext4_ext_get_actual_len(ex); >> + =A0 =A0 uninitialized =3D ext4_ext_is_uninitialized(ex); >> + >> + =A0 =A0 if (map->m_lblk + map->m_len < ee_block + ee_len) { >> + =A0 =A0 =A0 =A0 =A0 =A0 split_flag1 =3D split_flag & EXT4_EXT_MAY_= ZEROOUT ? >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 EXT4_EXT_MAY_Z= EROOUT : 0; >> + =A0 =A0 =A0 =A0 =A0 =A0 flags1 =3D flags | EXT4_GET_BLOCKS_PRE_IO; >> + =A0 =A0 =A0 =A0 =A0 =A0 if (uninitialized) >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 split_flag1 |=3D EXT4_EXT_= MARK_UNINIT1 | >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= =A0EXT4_EXT_MARK_UNINIT2; >> + =A0 =A0 =A0 =A0 =A0 =A0 err =3D ext4_split_extent_at(handle, inode= , path, >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 map->m_lbl= k + map->m_len, split_flag1, flags1); >> + =A0 =A0 } >> + Thank you for looking into the patch. =46irst, I think I need to explain split_flag added in the patch. Ther= e are three flags in split_flag1. 1.EXT4_EXT_MAY_ZEROOUT means whole extent can be zeroouted instead of splitting when splitting fails due to ENOSPACE; 2.EXT4_EXT_MARK_UNINIT1 indicates that the 1st part extent should be marked uninitialized, otherwise initialized. 3.EXT4_EXT_MARK_UNINIT2 is similar to EXT4_EXT_MARK_UNINIT1, only difference is that it has effect on the 2nd extent. > > Hmm, I could not see the zeroout extent gets marked as initialized he= re. > Nothing wrong to expose the wrong data, but certainly we are not take > advantage of zero out, =A0Perhaps I missed something? Here the extent [ee_block, ee_block + ee_len) is split into two extents [ee_block, map->m_lblk + map->m_len) and [map->m_lblk + map->m_len, ee_block + ee_len), which are marked same as ex. > > It would be nice to add some comments to describe the difference of > split_flag1, flags1, flags:-) Thanks. > > Also, I think we miss error handling here. What if the first split > failed and return error here? we still proceed to to do next split? I > think we should go to the err exit, isnt? Yes, error handling is missed. > > >> + =A0 =A0 ext4_ext_drop_refs(path); >> + =A0 =A0 path =3D ext4_ext_find_extent(inode, map->m_lblk, path); >> + =A0 =A0 if (IS_ERR(path)) >> + =A0 =A0 =A0 =A0 =A0 =A0 return PTR_ERR(path); >> + >> + =A0 =A0 if (map->m_lblk >=3D ee_block) { >> + =A0 =A0 =A0 =A0 =A0 =A0 split_flag1 =3D split_flag & EXT4_EXT_MAY_= ZEROOUT ? >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 EXT4_EXT_MAY_Z= EROOUT : 0; >> + =A0 =A0 =A0 =A0 =A0 =A0 if (uninitialized) >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 split_flag1 |=3D EXT4_EXT_= MARK_UNINIT1; >> + =A0 =A0 =A0 =A0 =A0 =A0 if (split_flag & EXT4_EXT_MARK_UNINIT2) >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 split_flag1 |=3D EXT4_EXT_= MARK_UNINIT2; Up to now, zeroout part will be marked initialized. >> + =A0 =A0 =A0 =A0 =A0 =A0 err =3D ext4_split_extent_at(handle, inode= , path, >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 map->m_lbl= k, split_flag1, flags); >> + =A0 =A0 =A0 =A0 =A0 =A0 if (err) >> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto out; >> + =A0 =A0 } >> + >> + =A0 =A0 ext4_ext_show_leaf(inode, path); >> +out: >> + =A0 =A0 return err ? err : map->m_len; >> +} >> + >> =A0#define EXT4_EXT_ZERO_LEN 7 >> =A0/* >> =A0 * This function is called by ext4_ext_map_blocks() if someone tr= ies to write > > > --=20 Best Wishes Yongqiang Yang -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html