On Tue 01-07-25 11:32:23, Baokun Li wrote: > On 2025/7/1 1:41, Jan Kara wrote: > > On Mon 30-06-25 18:02:49, Baokun Li wrote: > > > On 2025/6/30 16:38, Jan Kara wrote: > > > > We could make streaming goal to be ext4_fsblk_t so that also offset of the > > > > last big allocation in the group is recorded as I wrote above. That would > > > > tend to pack big allocations in each group together which is benefitial to > > > > combat fragmentation even with higher proportion of groups that are streaming > > > > goals (and likely becomes more important as the blocksize and thus group > > > > size grow). We can discuss proper number of slots for streaming allocation > > > > (I'm not hung up on it being quarter of the group count) but I'm convinced > > > > sb->s_groups_count is too much :) > > > > > > > > Honza > > > I think sbi->s_groups_count / 4 is indeed acceptable. However, I don't > > > believe recording offsets is necessary. As groups become larger, > > > contention for groups will intensify, and adding offsets would only > > > make this contention worse. > > I agree the contention for groups will increase when the group count goes > > down. I just thought offsets may help to find free space faster in large > > groups (and thus reduce contention) and also reduce free space > > fragmentation within a group (by having higher chances of placing large > > allocations close together within a group) but maybe that's not the case. > > Offsets are definitely not requirement at this point. > > > > Honza > > > Thinking this over, with LBS support coming, if our block size jumps from > 4KB to 64KB, the maximum group size will dramatically increase from 128MB > to 32GB (even with the current 4GB group limit). If free space within a > group gets heavily fragmented, iterating through that single group could > become quite time-consuming. > > Your idea of recording offsets to prevent redundant scanning of > already-checked extents within a group definitely makes sense. But with > reference to the idea of optimizing linear traversal of groups, I think it > might be better to record the offset of the first occurrence of each order > in the same way that bb_counters records the number of each order. Yes, something like that makes sense. But I guess that's a material for the next patch set :) Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
