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[Qemu-devel] [PATCH 7/7] 9p: v9fs fix calculation of max number of merge
From: |
edward . shishkin |
Subject: |
[Qemu-devel] [PATCH 7/7] 9p: v9fs fix calculation of max number of merged pages |
Date: |
Mon, 12 Dec 2016 19:15:42 +0100 |
From: Eduard Shishkin <address@hidden>
Don't merge too many pages when composing a 9p message because:
. it doesn't lead to essential performance improvement;
. to not allow user space to allocate big amount of kernel memory.
We use a limit of 256K (for total size of all pages merged per message),
as larger values don't provide any visible speedup.
Signed-off-by: Eduard Shishkin <address@hidden>
---
fs/9p/v9fs.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 58bff9e..50a4034 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -319,6 +319,8 @@ void put_flush_set(struct v9fs_flush_set *fset)
kfree(fset);
}
+#define MAX_FLUSH_DATA_SIZE (262144)
+
/**
* Allocate and initalize flush set
* Pre-conditions: valid msize is set
@@ -333,6 +335,11 @@ int alloc_init_flush_set(struct v9fs_session_info *v9ses)
if (num_pages < 2)
/* speedup impossible */
return 0;
+ if (num_pages > (MAX_FLUSH_DATA_SIZE >> PAGE_SHIFT))
+ /*
+ * no performance gain with larger values
+ */
+ num_pages = MAX_FLUSH_DATA_SIZE >> PAGE_SHIFT;
fset = kzalloc(sizeof(*fset), GFP_KERNEL);
if (!fset)
goto error;
--
2.7.4
- [Qemu-devel] [RFC][PATCH 0/7] 9p: v9fs read and write speedup - V2, Edward Shishkin, 2016/12/12
- [Qemu-devel] [PATCH 1/7] 9p: v9fs add writepages., edward . shishkin, 2016/12/12
- [Qemu-devel] [PATCH 5/7] 9p: v9fs fix semicolon.cocci warnings, edward . shishkin, 2016/12/12
- [Qemu-devel] [PATCH 6/7] 9p: v9fs fix readpages writepages contexts allocation, edward . shishkin, 2016/12/12
- [Qemu-devel] [PATCH 7/7] 9p: v9fs fix calculation of max number of merged pages,
edward . shishkin <=
- [Qemu-devel] [PATCH 3/7] 9p: v9fs fix ifnullfree.cocci warnings, edward . shishkin, 2016/12/12
- [Qemu-devel] [PATCH 4/7] 9p: v9fs fix odd_ptr_err.cocci warnings, edward . shishkin, 2016/12/12
- [Qemu-devel] [PATCH 2/7] 9p: v9fs new readpages., edward . shishkin, 2016/12/12