On Fri 17-02-23 17:44:15, Ojaswin Mujoo wrote: > When the length of best extent found is less than the length of goal extent > we need to make sure that the best extent atleast covers the start of the > original request. This is done by adjusting the ac_b_ex.fe_logical (logical > start) of the extent. > > While doing so, the current logic sometimes results in the best extent's logical > range overflowing the goal extent. Since this best extent is later added to the > inode preallocation list, we have a possibility of introducing overlapping > preallocations. This is discussed in detail here [1]. > > To fix this, replace the existing logic with the below logic for adjusting best > extent as it keeps fragmentation in check while ensuring logical range of best > extent doesn't overflow out of goal extent: > > 1. Check if best extent can be kept at end of goal range and still cover > original start. > 2. Else, check if best extent can be kept at start of goal range and still cover > original start. > 3. Else, keep the best extent at start of original request. > > Also, add a few extra BUG_ONs that might help catch errors faster. > > [1] https://lore.kernel.org/r/Y+OGkVvzPN0RMv0O@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx > > Signed-off-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx> Looks good to me. Feel free to add: Reviewed-by: Jan Kara <jack@xxxxxxx> Just one style nit below. > + /* > + * Use the below logic for adjusting best extent as it keeps > + * fragmentation in check while ensuring logical range of best > + * extent doesn't overflow out of goal extent: > + * > + * 1. Check if best ex can be kept at end of goal and still > + * cover original start > + * 2. Else, check if best ex can be kept at start of goal and > + * still cover original start > + * 3. Else, keep the best ex at start of original request. > + */ > + new_bex_end = ac->ac_g_ex.fe_logical + > + EXT4_C2B(sbi, ac->ac_g_ex.fe_len); > + new_bex_start = new_bex_end - EXT4_C2B(sbi, ac->ac_b_ex.fe_len); > + if (ac->ac_o_ex.fe_logical >= new_bex_start) > + goto adjust_bex; ^^^ The indentation looks too big here -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
