[PATCH v2 13/16] erofs: try to leave (de)compressed_pages on stack if possible

From: Gao Xiang
Date: Fri Jul 15 2022 - 11:43:29 EST


For the most cases, small pclusters can be decompressed with page
arrays on stack.

Try to leave both (de)compressed_pages on stack if possible as before.

Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
---
fs/erofs/zdata.c | 34 +++++++++++++++++++++-------------
1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 1cf377ed1452..d93ba0adcf9e 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -858,6 +858,7 @@ struct z_erofs_decompress_backend {
struct page **compressed_pages;

struct page **pagepool;
+ unsigned int onstack_used;
};

static int z_erofs_parse_out_bvecs(struct z_erofs_decompress_backend *be)
@@ -904,14 +905,9 @@ static int z_erofs_parse_in_bvecs(struct z_erofs_decompress_backend *be,
{
struct z_erofs_pcluster *pcl = be->pcl;
unsigned int pclusterpages = z_erofs_pclusterpages(pcl);
- struct page **compressed_pages;
int i, err = 0;

- /* XXX: will have a better approach in the following commits */
- compressed_pages = kmalloc_array(pclusterpages, sizeof(struct page *),
- GFP_KERNEL | __GFP_NOFAIL);
*overlapped = false;
-
for (i = 0; i < pclusterpages; ++i) {
struct z_erofs_bvec *bvec = &pcl->compressed_bvecs[i];
struct page *page = bvec->page;
@@ -922,7 +918,7 @@ static int z_erofs_parse_in_bvecs(struct z_erofs_decompress_backend *be,
DBG_BUGON(1);
continue;
}
- compressed_pages[i] = page;
+ be->compressed_pages[i] = page;

if (z_erofs_is_inline_pcluster(pcl)) {
if (!PageUptodate(page))
@@ -953,11 +949,8 @@ static int z_erofs_parse_in_bvecs(struct z_erofs_decompress_backend *be,
}
}

- if (err) {
- kfree(compressed_pages);
+ if (err)
return err;
- }
- be->compressed_pages = compressed_pages;
return 0;
}

@@ -976,15 +969,28 @@ static int z_erofs_decompress_pcluster(struct z_erofs_decompress_backend *be,
mutex_lock(&pcl->lock);
nr_pages = pcl->nr_pages;

+ /* allocate (de)compressed page arrays if cannot be kept on stack */
+ be->decompressed_pages = NULL;
+ be->compressed_pages = NULL;
+ be->onstack_used = 0;
if (nr_pages <= Z_EROFS_ONSTACK_PAGES) {
be->decompressed_pages = be->onstack_pages;
+ be->onstack_used = nr_pages;
memset(be->decompressed_pages, 0,
sizeof(struct page *) * nr_pages);
- } else {
+ }
+
+ if (pclusterpages + be->onstack_used <= Z_EROFS_ONSTACK_PAGES)
+ be->compressed_pages = be->onstack_pages + be->onstack_used;
+
+ if (!be->decompressed_pages)
be->decompressed_pages =
kvcalloc(nr_pages, sizeof(struct page *),
GFP_KERNEL | __GFP_NOFAIL);
- }
+ if (!be->compressed_pages)
+ be->compressed_pages =
+ kvcalloc(pclusterpages, sizeof(struct page *),
+ GFP_KERNEL | __GFP_NOFAIL);

err2 = z_erofs_parse_out_bvecs(be);
if (err2)
@@ -1041,7 +1047,9 @@ static int z_erofs_decompress_pcluster(struct z_erofs_decompress_backend *be,
WRITE_ONCE(pcl->compressed_bvecs[i].page, NULL);
}
}
- kfree(be->compressed_pages);
+ if (be->compressed_pages < be->onstack_pages ||
+ be->compressed_pages >= be->onstack_pages + Z_EROFS_ONSTACK_PAGES)
+ kvfree(be->compressed_pages);

for (i = 0; i < nr_pages; ++i) {
page = be->decompressed_pages[i];
--
2.24.4