Re: [PATCH v4] erofs: free pclusters if no cached folio attached

From: Gao Xiang
Date: Mon Nov 11 2024 - 21:32:53 EST


Just two extra minor nits...

First, the subject line would be
"erofs: free pclusters if no cached folio is attached"

On 2024/11/11 19:38, Chunhai Guo wrote:
Once a pcluster is fully decompressed and there are no attached cached
folios, its corresponding `struct z_erofs_pcluster` will be freed. This
will significantly reduce the frequency of calls to erofs_shrink_scan()
and the memory allocated for `struct z_erofs_pcluster`.

The tables below show approximately a 96% reduction in the calls to
erofs_shrink_scan() and in the memory allocated for `struct
z_erofs_pcluster` after applying this patch. The results were obtained
by performing a test to copy a 4.1GB partition on ARM64 Android devices
running the 6.6 kernel with an 8-core CPU and 12GB of memory.

1. The reduction in calls to erofs_shrink_scan():
+-----------------+-----------+----------+---------+
| | w/o patch | w/ patch | diff |
+-----------------+-----------+----------+---------+
| Average (times) | 11390 | 390 | -96.57% |
+-----------------+-----------+----------+---------+

2. The reduction in memory released by erofs_shrink_scan():
+-----------------+-----------+----------+---------+
| | w/o patch | w/ patch | diff |
+-----------------+-----------+----------+---------+
| Average (Byte) | 133612656 | 4434552 | -96.68% |
+-----------------+-----------+----------+---------+

Signed-off-by: Chunhai Guo <guochunhai@xxxxxxxx>

...

-static void z_erofs_put_pcluster(struct z_erofs_pcluster *pcl)
+static void z_erofs_put_pcluster(struct erofs_sb_info *sbi,
+ struct z_erofs_pcluster *pcl, bool try_free)
{
+ bool free = false;
+
if (lockref_put_or_lock(&pcl->lockref))
return;
DBG_BUGON(__lockref_is_dead(&pcl->lockref));
- if (pcl->lockref.count == 1)
- atomic_long_inc(&erofs_global_shrink_cnt);
- --pcl->lockref.count;
+ if (--pcl->lockref.count == 0) {

Second, EROFS codebase uses `!--pcl->lockref.count`
coding style instead of `== 0` since the old checkpatch.pl
will complain this and I'd like to keep consistentency..

Otherwise it looks good to me, if you send out a
new version, I will apply directly.

Thanks,
Gao Xiang