+ squashfs-dont-allocate-read_page-cache-if-squashfs_file_direct-configured.patch added to mm-nonmm-unstable branch

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

The patch titled
     Subject: squashfs: don't allocate read_page cache if SQUASHFS_FILE_DIRECT configured
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     squashfs-dont-allocate-read_page-cache-if-squashfs_file_direct-configured.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/squashfs-dont-allocate-read_page-cache-if-squashfs_file_direct-configured.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Phillip Lougher <phillip@squashfs.org.uk>
Subject: squashfs: don't allocate read_page cache if SQUASHFS_FILE_DIRECT configured
Date: Sun, 29 Dec 2024 23:37:50 +0000

If Squashfs has been configured to directly read datablocks into the page
cache (SQUASHFS_FILE_DIRECT), then the read_page cache is unnecessary.

This improvement is due to the following two commits, which added the
ability to read datablocks into the page cache when pages were missing,
enabling the fallback which used an intermediate buffer to be removed.

commit f268eedddf359 ("squashfs: extend "page actor" to handle missing pages")
commit 1bb1a07afad97 ("squashfs: don't use intermediate buffer if pages missing")

This reduces the amount of memory used when mounting a filesystem by
block_size * maximum number of threads.

Link: https://lkml.kernel.org/r/20241229233752.54481-3-phillip@squashfs.org.uk
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/squashfs/squashfs.h |    6 ++++++
 fs/squashfs/super.c    |    2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

--- a/fs/squashfs/squashfs.h~squashfs-dont-allocate-read_page-cache-if-squashfs_file_direct-configured
+++ a/fs/squashfs/squashfs.h
@@ -14,6 +14,12 @@
 
 #define WARNING(s, args...)	pr_warn("SQUASHFS: "s, ## args)
 
+#ifdef CONFIG_SQUASHFS_FILE_CACHE
+#define SQUASHFS_READ_PAGES msblk->max_thread_num
+#else
+#define SQUASHFS_READ_PAGES 0
+#endif
+
 /* block.c */
 extern int squashfs_read_data(struct super_block *, u64, int, u64 *,
 				struct squashfs_page_actor *);
--- a/fs/squashfs/super.c~squashfs-dont-allocate-read_page-cache-if-squashfs_file_direct-configured
+++ a/fs/squashfs/super.c
@@ -323,7 +323,7 @@ static int squashfs_fill_super(struct su
 
 	/* Allocate read_page block */
 	msblk->read_page = squashfs_cache_init("data",
-		msblk->max_thread_num, msblk->block_size);
+		SQUASHFS_READ_PAGES, msblk->block_size);
 	if (IS_ERR(msblk->read_page)) {
 		errorf(fc, "Failed to allocate read_page block");
 		err = PTR_ERR(msblk->read_page);
_

Patches currently in -mm which might be from phillip@squashfs.org.uk are

squashfs-make-squashfs_cache_init-return-err_ptr-enomem.patch
squashfs-dont-allocate-read_page-cache-if-squashfs_file_direct-configured.patch
documentation-update-the-squashfs-filesystem-documentation.patch
squashfs-update-kconfig-information.patch