The patch titled
Subject: squashfs: don't use intermediate buffer if pages missing
has been added to the -mm mm-nonmm-unstable branch. Its filename is
squashfs-dont-use-intermediate-buffer-if-pages-missing.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/squashfs-dont-use-intermediate-buffer-if-pages-missing.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@xxxxxxxxxxxxxxx>
Subject: squashfs: don't use intermediate buffer if pages missing
Date: Sat, 11 Jun 2022 04:21:33 +0100
Now that the "page actor" can handle missing pages, we don't have to fall
back to using an intermediate buffer in Squashfs_readpage_block() if all
the pages necessary can't be obtained.
Link: https://lkml.kernel.org/r/20220611032133.5743-3-phillip@xxxxxxxxxxxxxxx
Signed-off-by: Phillip Lougher <phillip@xxxxxxxxxxxxxxx>
Cc: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Xiongwei Song <Xiongwei.Song@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/squashfs/file_direct.c | 75 +++++-------------------------------
1 file changed, 12 insertions(+), 63 deletions(-)
--- a/fs/squashfs/file_direct.c~squashfs-dont-use-intermediate-buffer-if-pages-missing
+++ a/fs/squashfs/file_direct.c
@@ -18,9 +18,6 @@
#include "squashfs.h"
#include "page_actor.h"
-static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
- int pages, struct page **page, int bytes);
-
/* Read separately compressed datablock directly into page cache */
int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
int expected)
@@ -33,7 +30,7 @@ int squashfs_readpage_block(struct page
int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
int start_index = target_page->index & ~mask;
int end_index = start_index | mask;
- int i, n, pages, missing_pages, bytes, res = -ENOMEM;
+ int i, n, pages, bytes, res = -ENOMEM;
struct page **page;
struct squashfs_page_actor *actor;
void *pageaddr;
@@ -48,44 +45,29 @@ int squashfs_readpage_block(struct page
return res;
/* Try to grab all the pages covered by the Squashfs block */
- for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) {
+ for (i = 0, n = start_index; n <= end_index; n++) {
page[i] = (n == target_page->index) ? target_page :
grab_cache_page_nowait(target_page->mapping, n);
- if (page[i] == NULL) {
- missing_pages++;
+ if (page[i] == NULL)
continue;
- }
if (PageUptodate(page[i])) {
unlock_page(page[i]);
put_page(page[i]);
- page[i] = NULL;
- missing_pages++;
+ continue;
}
- }
-
- if (missing_pages) {
- /*
- * Couldn't get one or more pages, this page has either
- * been VM reclaimed, but others are still in the page cache
- * and uptodate, or we're racing with another thread in
- * squashfs_readpage also trying to grab them. Fall back to
- * using an intermediate buffer.
- */
- res = squashfs_read_cache(target_page, block, bsize, pages,
- page, expected);
- if (res < 0)
- goto mark_errored;
- goto out;
+ i++;
}
+ pages = i;
+
/*
* Create a "page actor" which will kmap and kunmap the
* page cache pages appropriately within the decompressor
*/
- actor = squashfs_page_actor_init_special(msblk, page, pages, 0);
+ actor = squashfs_page_actor_init_special(msblk, page, pages, expected);
if (actor == NULL)
goto out;
@@ -102,12 +84,12 @@ int squashfs_readpage_block(struct page
goto mark_errored;
}
- /* Last page may have trailing bytes not filled */
+ /* Last page (if present) may have trailing bytes not filled */
bytes = res % PAGE_SIZE;
- if (bytes) {
- pageaddr = kmap_atomic(page[pages - 1]);
+ if (page[pages - 1]->index == end_index && bytes) {
+ pageaddr = kmap_local_page(page[pages - 1]);
memset(pageaddr + bytes, 0, PAGE_SIZE - bytes);
- kunmap_atomic(pageaddr);
+ kunmap_local(pageaddr);
}
/* Mark pages as uptodate, unlock and release */
@@ -140,36 +122,3 @@ out:
kfree(page);
return res;
}
-
-
-static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
- int pages, struct page **page, int bytes)
-{
- struct inode *i = target_page->mapping->host;
- struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
- block, bsize);
- int res = buffer->error, n, offset = 0;
-
- if (res) {
- ERROR("Unable to read page, block %llx, size %x\n", block,
- bsize);
- goto out;
- }
-
- for (n = 0; n < pages && bytes > 0; n++,
- bytes -= PAGE_SIZE, offset += PAGE_SIZE) {
- int avail = min_t(int, bytes, PAGE_SIZE);
-
- if (page[n] == NULL)
- continue;
-
- squashfs_fill_page(page[n], buffer, offset, avail);
- unlock_page(page[n]);
- if (page[n] != target_page)
- put_page(page[n]);
- }
-
-out:
- squashfs_cache_put(buffer);
- return res;
-}
_
Patches currently in -mm which might be from phillip@xxxxxxxxxxxxxxx are
squashfs-extend-page-actor-to-handle-missing-pages.patch
squashfs-dont-use-intermediate-buffer-if-pages-missing.patch
