Commit 2e227ff5 authored by Chanho Min's avatar Chanho Min Committed by Andrew Morton
Browse files

squashfs: add optional full compressed block caching 

The commit 93e72b3c ("squashfs: migrate from ll_rw_block usage
to BIO") removed caching of compressed blocks in SquashFS, causing fio
performance regression in workloads with repeated file reads.  Without
caching, every read triggers disk I/O, severely impacting performance in
tools like fio.

This patch introduces a new CONFIG_SQUASHFS_COMP_CACHE_FULL Kconfig option
to enable caching of all compressed blocks, restoring performance to
pre-BIO migration levels.  When enabled, all pages in a BIO are cached in
the page cache, reducing disk I/O for repeated reads.  The fio test
results with this patch confirm the performance restoration:

For example, fio tests (iodepth=1, numjobs=1,
ioengine=psync) show a notable performance restoration:

Disable CONFIG_SQUASHFS_COMP_CACHE_FULL:
  IOPS=815, BW=102MiB/s (107MB/s)(6113MiB/60001msec)
Enable CONFIG_SQUASHFS_COMP_CACHE_FULL:
  IOPS=2223, BW=278MiB/s (291MB/s)(16.3GiB/59999msec)

The tradeoff is increased memory usage due to caching all compressed
blocks.  The CONFIG_SQUASHFS_COMP_CACHE_FULL option allows users to enable
this feature selectively, balancing performance and memory usage for
workloads with frequent repeated reads.

Link: https://lkml.kernel.org/r/20250521072559.2389-1-chanho.min@lge.com


Signed-off-by: default avatarChanho Min <chanho.min@lge.com>
Reviewed-by Phillip Lougher <phillip@squashfs.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 4496e1c1

fs/squashfs/Kconfig

+21 −0
Original line number Diff line number Diff line
@@ -149,6 +149,27 @@ config SQUASHFS_XATTR 


	  If unsure, say N.



config SQUASHFS_COMP_CACHE_FULL

	bool "Enable full caching of compressed blocks"

	depends on SQUASHFS

	default n

	help

	  This option enables caching of all compressed blocks, Without caching,

	  repeated reads of the same files trigger excessive disk I/O, significantly

	  reducinng performance in workloads like fio-based benchmarks.



	  For example, fio tests (iodepth=1, numjobs=1, ioengine=psync) show:

	   With caching: IOPS=2223, BW=278MiB/s (291MB/s)

	   Without caching: IOPS=815, BW=102MiB/s (107MB/s)



	  Enabling this option restores performance to pre-regression levels by

	  caching all compressed blocks in the page cache, reducing disk I/O for

	  repeated reads. However, this increases memory usage, which may be a

	  concern in memory-constrained environments.



	  Enable this option if your workload involves frequent repeated reads and

	  memory usage is not a limiting factor. If unsure, say N.



config SQUASHFS_ZLIB

	bool "Include support for ZLIB compressed file systems"

	depends on SQUASHFS

fs/squashfs/block.c

+28 −0
Original line number Diff line number Diff line
@@ -88,6 +88,10 @@ static int squashfs_bio_read_cached(struct bio *fullbio, 
	struct bio_vec *bv;

	int idx = 0;

	int err = 0;

#ifdef CONFIG_SQUASHFS_COMP_CACHE_FULL

	struct page **cache_pages = kmalloc_array(page_count,

			sizeof(void *), GFP_KERNEL | __GFP_ZERO);

#endif



	bio_for_each_segment_all(bv, fullbio, iter_all) {

		struct page *page = bv->bv_page;
@@ -110,6 +114,11 @@ static int squashfs_bio_read_cached(struct bio *fullbio, 
			head_to_cache = page;

		else if (idx == page_count - 1 && index + length != read_end)

			tail_to_cache = page;

#ifdef CONFIG_SQUASHFS_COMP_CACHE_FULL

		/* Cache all pages in the BIO for repeated reads */

		else if (cache_pages)

			cache_pages[idx] = page;

#endif



		if (!bio || idx != end_idx) {

			struct bio *new = bio_alloc_clone(bdev, fullbio,
@@ -163,6 +172,25 @@ static int squashfs_bio_read_cached(struct bio *fullbio, 
		}

	}



#ifdef CONFIG_SQUASHFS_COMP_CACHE_FULL

	if (!cache_pages)

		goto out;



	for (idx = 0; idx < page_count; idx++) {

		if (!cache_pages[idx])

			continue;

		int ret = add_to_page_cache_lru(cache_pages[idx], cache_mapping,

						(read_start >> PAGE_SHIFT) + idx,

						GFP_NOIO);



		if (!ret) {

			SetPageUptodate(cache_pages[idx]);

			unlock_page(cache_pages[idx]);

		}

	}

	kfree(cache_pages);

out:

#endif

	return 0;

}