[<prev] [next>] [day] [month] [year] [list]
Message-Id: <20250502081947.44034-1-chanho.min@lge.com>
Date: Fri, 2 May 2025 17:19:47 +0900
From: Chanho Min <chanho.min@....com>
To: Phillip Lougher <phillip@...ashfs.org.uk>
Cc: linux-kernel@...r.kernel.org,
gunho.lee@....com,
Chanho Min <chanho.min@....com>
Subject: [PATCH] squashfs: Add optional full compressed block caching
The commit 93e72b3c612adcaca1("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 trade-off 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.
Signed-off-by: Chanho Min <chanho.min@....com>
---
fs/squashfs/Kconfig | 21 +++++++++++++++++++++
fs/squashfs/block.c | 28 ++++++++++++++++++++++++++++
2 files changed, 49 insertions(+)
diff --git a/fs/squashfs/Kconfig b/fs/squashfs/Kconfig
index 60fc98bdf421..cc5e4be58afa 100644
--- a/fs/squashfs/Kconfig
+++ b/fs/squashfs/Kconfig
@@ -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:
+ Without caching: IOPS=2223, BW=278MiB/s (291MB/s)
+ With 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
diff --git a/fs/squashfs/block.c b/fs/squashfs/block.c
index 2dc730800f44..3061043e915c 100644
--- a/fs/squashfs/block.c
+++ b/fs/squashfs/block.c
@@ -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;
}
--
2.17.1
Powered by blists - more mailing lists