Re: [PATCH v2 00/16] Parallelizing filesystem writeback

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 14 Oct 2025 17:38:29 +0530 Kundan Kumar <kundan.kumar@samsung.com> wrote:

> Currently, pagecache writeback is performed by a single thread. Inodes
> are added to a dirty list, and delayed writeback is triggered. The single
> writeback thread then iterates through the dirty inode list, and executes
> the writeback.
> 
> This series parallelizes the writeback by allowing multiple writeback
> contexts per backing device (bdi). These writeback contexts are executed
> as separate, independent threads, improving overall parallelism. Inodes
> are distributed to these threads and are flushed in parallel.
> 
> ...
>
> IOPS and throughput
> ===================
> With the affinity to allocation group we see significant improvement in
> XFS when we write to multiple files in different directories(AGs).
> 
> Performance gains:
>   A) Workload 12 files each of 1G in 12 directories(AGs) - numjobs = 12
>     - NVMe device BM1743 SSD
>         Base XFS                : 243 MiB/s
>         Parallel Writeback XFS  : 759 MiB/s  (+212%)
> 
>     - NVMe device PM9A3 SSD
>         Base XFS                : 368 MiB/s
>         Parallel Writeback XFS  : 1634 MiB/s  (+344%)
> 
>   B) Workload 6 files each of 20G in 6 directories(AGs)  - numjobs = 6
>     - NVMe device BM1743 SSD
>         Base XFS                : 305 MiB/s
>         Parallel Writeback XFS  : 706 MiB/s  (+131%)
> 
>     - NVMe device PM9A3 SSD
>         Base XFS                : 315 MiB/s
>         Parallel Writeback XFS  : 990 MiB/s  (+214%)
> 
> Filesystem fragmentation
> ========================
> We also see that there is no increase in filesystem fragmentation
> Number of extents per file:
>   A) Workload 6 files each 1G in single directory(AG)   - numjobs = 1
>         Base XFS                : 17
>         Parallel Writeback XFS  : 17
> 
>   B) Workload 12 files each of 1G to 12 directories(AGs)- numjobs = 12
>         Base XFS                : 166593
>         Parallel Writeback XFS  : 161554
> 
>   C) Workload 6 files each of 20G to 6 directories(AGs) - numjobs = 6
>         Base XFS                : 3173716
>         Parallel Writeback XFS  : 3364984

Nice results.  Is testing planned for other filesystems?