| 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
| ||
|
Date: Fri, 11 Jun 2010 15:26:20 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
Andi Kleen <ak@...ux.intel.com>,
Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v2 1/2] tmpfs: Quick token library to allow scalable
retrieval of tokens from token jar
On Fri, 11 Jun 2010 15:06:43 -0700
Tim Chen <tim.c.chen@...ux.intel.com> wrote:
> > afacit, your proposed implementation could have used percpu_counters.
> > If so, that would be by far the best way of doing it, because that
> > doesn't require the addition of new infrastructure.
>
> Just having percpu counters is not enough.
> There is additional logic required to manage the per cpu counters:
> (1) set limit on the total number of tokens (2) distribute tokens into
> per cpu counter (3) logic to coordinate where to get additional tokens
> when we run out of tokens in the per cpu counter. (4) rebalance the
> tokens when we have too many of the tokens returned to a per cpu
> counter. I'm trying to encapsulate these logic into the library.
> Otherwise, these logic will still need to be duplicated in the code
> using the per cpu counters.
There's no need for any of that.
free_blocks is just a counter. You add things to it, you subtract
things from it and you compare it with a threshold.
Something like the below.
It a bit buggy - using percpu_counter_init() against an
already-initialised percpu_counter() is leaky. I suspect that's
happening in remount_fs.
A better approach would be to remove free_blocks altogether and add a
new `percpu_counter used_blocks;' which simply counts how many blocks
are presently in use. Such a thing would then never need to be
reinitialised.
include/linux/shmem_fs.h | 3 ++-
mm/shmem.c | 20 +++++++++++---------
2 files changed, 13 insertions(+), 10 deletions(-)
diff -puN mm/shmem.c~a mm/shmem.c
--- a/mm/shmem.c~a
+++ a/mm/shmem.c
@@ -28,6 +28,7 @@
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/module.h>
+#include <linux/percpu_counter.h>
#include <linux/swap.h>
static struct vfsmount *shm_mnt;
@@ -233,8 +234,8 @@ static void shmem_free_blocks(struct ino
{
struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
if (sbinfo->max_blocks) {
+ percpu_counter_add(&sbinfo->free_blocks, pages);
spin_lock(&sbinfo->stat_lock);
- sbinfo->free_blocks += pages;
inode->i_blocks -= pages*BLOCKS_PER_PAGE;
spin_unlock(&sbinfo->stat_lock);
}
@@ -422,11 +423,11 @@ static swp_entry_t *shmem_swp_alloc(stru
*/
if (sbinfo->max_blocks) {
spin_lock(&sbinfo->stat_lock);
- if (sbinfo->free_blocks <= 1) {
+ if (percpu_counter_read(&sbinfo->free_blocks) <= 1) {
spin_unlock(&sbinfo->stat_lock);
return ERR_PTR(-ENOSPC);
}
- sbinfo->free_blocks--;
+ percpu_counter_dec(&sbinfo->free_blocks);
inode->i_blocks += BLOCKS_PER_PAGE;
spin_unlock(&sbinfo->stat_lock);
}
@@ -1389,14 +1390,14 @@ repeat:
sbinfo = SHMEM_SB(inode->i_sb);
if (sbinfo->max_blocks) {
spin_lock(&sbinfo->stat_lock);
- if (sbinfo->free_blocks == 0 ||
+ if (percpu_counter_read(&sbinfo->free_blocks) <= 0 ||
shmem_acct_block(info->flags)) {
spin_unlock(&sbinfo->stat_lock);
spin_unlock(&info->lock);
error = -ENOSPC;
goto failed;
}
- sbinfo->free_blocks--;
+ percpu_counter_dec(&sbinfo->free_blocks);
inode->i_blocks += BLOCKS_PER_PAGE;
spin_unlock(&sbinfo->stat_lock);
} else if (shmem_acct_block(info->flags)) {
@@ -1795,7 +1796,8 @@ static int shmem_statfs(struct dentry *d
spin_lock(&sbinfo->stat_lock);
if (sbinfo->max_blocks) {
buf->f_blocks = sbinfo->max_blocks;
- buf->f_bavail = buf->f_bfree = sbinfo->free_blocks;
+ buf->f_bavail = buf->f_bfree =
+ percpu_counter_read(&sbinfo->free_blocks);
}
if (sbinfo->max_inodes) {
buf->f_files = sbinfo->max_inodes;
@@ -2251,7 +2253,7 @@ static int shmem_remount_fs(struct super
return error;
spin_lock(&sbinfo->stat_lock);
- blocks = sbinfo->max_blocks - sbinfo->free_blocks;
+ blocks = sbinfo->max_blocks - percpu_counter_read(&sbinfo->free_blocks);
inodes = sbinfo->max_inodes - sbinfo->free_inodes;
if (config.max_blocks < blocks)
goto out;
@@ -2270,7 +2272,7 @@ static int shmem_remount_fs(struct super
error = 0;
sbinfo->max_blocks = config.max_blocks;
- sbinfo->free_blocks = config.max_blocks - blocks;
+ percpu_counter_init(&sbinfo->free_blocks, config.max_blocks - blocks);
sbinfo->max_inodes = config.max_inodes;
sbinfo->free_inodes = config.max_inodes - inodes;
@@ -2345,7 +2347,7 @@ int shmem_fill_super(struct super_block
#endif
spin_lock_init(&sbinfo->stat_lock);
- sbinfo->free_blocks = sbinfo->max_blocks;
+ percpu_counter_init(&sbinfo->free_blocks, sbinfo->max_blocks);
sbinfo->free_inodes = sbinfo->max_inodes;
sb->s_maxbytes = SHMEM_MAX_BYTES;
diff -puN include/linux/shmem_fs.h~a include/linux/shmem_fs.h
--- a/include/linux/shmem_fs.h~a
+++ a/include/linux/shmem_fs.h
@@ -3,6 +3,7 @@
#include <linux/swap.h>
#include <linux/mempolicy.h>
+#include <linux/percpu_counter.h>
/* inode in-kernel data */
@@ -23,7 +24,7 @@ struct shmem_inode_info {
struct shmem_sb_info {
unsigned long max_blocks; /* How many blocks are allowed */
- unsigned long free_blocks; /* How many are left for allocation */
+ struct percpu_counter free_blocks; /* How many are left for allocation */
unsigned long max_inodes; /* How many inodes are allowed */
unsigned long free_inodes; /* How many are left for allocation */
spinlock_t stat_lock; /* Serialize shmem_sb_info changes */
_
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists