linux-kernel - [PATCHv2 1/7] zram: free slot memory early during write

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20241218063513.297475-2-senozhatsky@chromium.org>
Date: Wed, 18 Dec 2024 15:34:18 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Minchan Kim <minchan@...nel.org>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCHv2 1/7] zram: free slot memory early during write

In the current implementation entry's previously allocated
memory is released in the very last moment, when we already
have allocated a new memory for new data.  This, basically,
temporarily increases memory usage for no good reason.  For
example, consider the case when both old (stale) and new
entry data are incompressible so such entry will temporarily
use two physical pages - one for stale (old) data and one
for new data.  We can release old memory as soon as we get
a write request for entry.

Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
 drivers/block/zram/zram_drv.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 45df5eeabc5e..cda0f3fd4058 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1648,6 +1648,11 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 	unsigned long element = 0;
 	enum zram_pageflags flags = 0;
 
+	/* First, free memory allocated to this slot (if any) */
+	zram_slot_lock(zram, index);
+	zram_free_page(zram, index);
+	zram_slot_unlock(zram, index);
+
 	mem = kmap_local_page(page);
 	if (page_same_filled(mem, &element)) {
 		kunmap_local(mem);
@@ -1736,13 +1741,7 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 	zs_unmap_object(zram->mem_pool, handle);
 	atomic64_add(comp_len, &zram->stats.compr_data_size);
 out:
-	/*
-	 * Free memory associated with this sector
-	 * before overwriting unused sectors.
-	 */
 	zram_slot_lock(zram, index);
-	zram_free_page(zram, index);
-
 	if (comp_len == PAGE_SIZE) {
 		zram_set_flag(zram, index, ZRAM_HUGE);
 		atomic64_inc(&zram->stats.huge_pages);
-- 
2.47.1.613.gc27f4b7a9f-goog