# Linux 7.4 cuts XFS checksumming overhead with lazy bounce buffers

> **Key takeaway:** Linux 7.4 replaces unconditional bounce buffering for XFS checksummed reads with a lazy approach that only allocates fallback buffers on actual checksum failures.

**Published:** 2026-10-20T17:05:28+00:00 
**Source:** Phoronix Benchmarks & Drivers 
**Category:** kernel-os 
**Canonical URL:** https://fosswire.org/news/linux-74-cuts-xfs-checksumming-overhead-with-lazy-bounce-buf.html 

## Summary
A VFS IOmap change merged for Linux 7.4 eliminates unconditional bounce buffering during checksummed direct reads on XFS. Previously, every such read triggered a bounce buffer allocation to prevent userspace buffer modification from corrupting in-flight data, consuming DRAM bandwidth and CPU cycles for copies rarely needed. The new code writes directly to the user buffer and only retries with a bounce buffer if checksum verification fails. Integrity checking also moves from IOmap into the filesystem layer, giving XFS direct control over error handling.

## What changes in the IOmap path
- **Before:** XFS unconditionally bounce-buffered every direct read on checksumming devices, using bio_vec allocations that produced smaller, unaligned I/Os (1 MB minus 4K with 4K pages)
- **After:** Reads go directly to the user buffer; bounce buffer allocated only on checksum failure
- **Integrity verification** moved from generic IOmap code into the filesystem layer so XFS handles errors directly
- **Stable pages requirement** still enforced, but without the speculative copy overhead
- No benchmark numbers were provided in the patch series to quantify the improvement

## Why it matters
XFS deployments with data integrity checking enabled—common in enterprise storage and NAS systems—should see reduced memory pressure and CPU usage under read-heavy workloads. The change may also improve I/O alignment for large reads.