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Subject[PATCH] ipc/shm.c: add RSS and swap size information to /proc/sysvipc/shm (v2)
The kernel currently provides no functionality to analyze the RSS
and swap space usage of each individual sysvipc shared memory segment.

This patch adds this info for each existing shm segment by extending
the output of /proc/sysvipc/shm by two columns for RSS and swap.

This additional info about RSS/swap usage of shm segments is very
useful for runtime analysis of the kernel. In my case, at work I'm taking
care of a large ERP enterprise software, which uses lots of big
shared memory segments (we often have Linux systems with >= 16GB shm
usage). Sometimes we get customer reports about "slow" system responses
and while looking into their configurations we often find massive
swapping activity on the system. With this patch it's now easy to see
from the command line if and which shm segments gets swapped out (and
how much) and we can more easily give recommendations for system tuning.
Without the patch it's currently not possible to do such shm analysis at
all.

Since shmctl(SHM_INFO) already provides a similiar calculation (it
currently sums up all RSS/swap info for all segments), I did split
out a static function which is now used by the /proc/sysvipc/shm
output and shmctl(SHM_INFO).
Additionally, the header line of /proc/sysvipc/shm was changed so
that all columns are adjusted correctly (the width of size field
is 10 chars for 32bit and 21 chars for 64bit kernels).

Tested on x86-64 and parisc (32- and 64bit).

Signed-off-by: Helge Deller <deller@gmx.de>
Acked-by: Hugh Dickins <hughd@google.com>

---
shm.c | 63
++++++++++++++++++++++++++++++++++++++++++---------------------
1 file changed, 42 insertions(+), 21 deletions(-)

diff --git a/ipc/shm.c b/ipc/shm.c
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -108,7 +108,11 @@ void __init shm_init (void)
{
shm_init_ns(&init_ipc_ns);
ipc_init_proc_interface("sysvipc/shm",
- " key shmid perms size cpid lpid nattch uid gid cuid cgid atime dtime ctime\n",
+#if BITS_PER_LONG <= 32
+ " key shmid perms size cpid lpid nattch uid gid cuid cgid atime dtime ctime rss swap\n",
+#else
+ " key shmid perms size cpid lpid nattch uid gid cuid cgid atime dtime ctime rss swap\n",
+#endif
IPC_SHM_IDS, sysvipc_shm_proc_show);
}

@@ -542,6 +546,34 @@ static inline unsigned long copy_shminfo_to_user(void __user *buf, struct shminf
}

/*
+ * Calculate and add used RSS and swap pages of a shm.
+ * Called with shm_ids.rw_mutex held as a reader
+ */
+static void shm_add_rss_swap(struct shmid_kernel *shp,
+ unsigned long *rss_add, unsigned long *swp_add)
+{
+ struct inode *inode;
+
+ inode = shp->shm_file->f_path.dentry->d_inode;
+
+ if (is_file_hugepages(shp->shm_file)) {
+ struct address_space *mapping = inode->i_mapping;
+ struct hstate *h = hstate_file(shp->shm_file);
+ *rss_add += pages_per_huge_page(h) * mapping->nrpages;
+ } else {
+#ifdef CONFIG_SHMEM
+ struct shmem_inode_info *info = SHMEM_I(inode);
+ spin_lock(&info->lock);
+ *rss_add += inode->i_mapping->nrpages;
+ *swp_add += info->swapped;
+ spin_unlock(&info->lock);
+#else
+ *rss_add += inode->i_mapping->nrpages;
+#endif
+ }
+}
+
+/*
* Called with shm_ids.rw_mutex held as a reader
*/
static void shm_get_stat(struct ipc_namespace *ns, unsigned long *rss,
@@ -558,30 +590,13 @@ static void shm_get_stat(struct ipc_namespace *ns, unsigned long *rss,
for (total = 0, next_id = 0; total < in_use; next_id++) {
struct kern_ipc_perm *ipc;
struct shmid_kernel *shp;
- struct inode *inode;

ipc = idr_find(&shm_ids(ns).ipcs_idr, next_id);
if (ipc == NULL)
continue;
shp = container_of(ipc, struct shmid_kernel, shm_perm);

- inode = shp->shm_file->f_path.dentry->d_inode;
-
- if (is_file_hugepages(shp->shm_file)) {
- struct address_space *mapping = inode->i_mapping;
- struct hstate *h = hstate_file(shp->shm_file);
- *rss += pages_per_huge_page(h) * mapping->nrpages;
- } else {
-#ifdef CONFIG_SHMEM
- struct shmem_inode_info *info = SHMEM_I(inode);
- spin_lock(&info->lock);
- *rss += inode->i_mapping->nrpages;
- *swp += info->swapped;
- spin_unlock(&info->lock);
-#else
- *rss += inode->i_mapping->nrpages;
-#endif
- }
+ shm_add_rss_swap(shp, rss, swp);

total++;
}
@@ -1070,6 +1085,9 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
static int sysvipc_shm_proc_show(struct seq_file *s, void *it)
{
struct shmid_kernel *shp = it;
+ unsigned long rss = 0, swp = 0;
+
+ shm_add_rss_swap(shp, &rss, &swp);

#if BITS_PER_LONG <= 32
#define SIZE_SPEC "%10lu"
@@ -1079,7 +1097,8 @@ static int sysvipc_shm_proc_show(struct seq_file *s, void *it)

return seq_printf(s,
"%10d %10d %4o " SIZE_SPEC " %5u %5u "
- "%5lu %5u %5u %5u %5u %10lu %10lu %10lu\n",
+ "%5lu %5u %5u %5u %5u %10lu %10lu %10lu "
+ SIZE_SPEC " " SIZE_SPEC "\n",
shp->shm_perm.key,
shp->shm_perm.id,
shp->shm_perm.mode,
@@ -1093,6 +1112,8 @@ static int sysvipc_shm_proc_show(struct seq_file *s, void *it)
shp->shm_perm.cgid,
shp->shm_atim,
shp->shm_dtim,
- shp->shm_ctim);
+ shp->shm_ctim,
+ rss * PAGE_SIZE,
+ swp * PAGE_SIZE);
}
#endif

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