Fix: Building the event list fails on fragmented memory

On a small arm imx6 solo with 256MB RAM it often happens that memory
becomes fragmented rather quickly, so that kmalloc will not be able to
get enough consecutive pages (enocuntered for example if you enable all
kernel events: lttng enable-event -k syscall --all).

This patch switches the allocation to vmalloc. Tested for x86 on Ubuntu
12.04 Lts and on imx6 solo 256MB RAM

If this patch is not applied, you can identify low and/or fragmented
memory failures by looking at the kernel ring buffer (please ignore DMA,
it is due to some memory setup misconfiguration, should read Normal):

...
[  321.993820] lttng-sessiond: page allocation failure: order:4, mode:0x1040d0
...
[  321.994711] lowmem_reserve[]: 0 0 0
[  321.994727] DMA: 801*4kB (UEMC) 424*8kB (EMC) 355*16kB (UEMC) 344*32kB (MC) 340*64kB (C) 8*128kB (C) 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB 0*8192kB 0*16384kB 0*32768kB = 46068kB

[ Edit by Mathieu: use vzalloc() rather than vmalloc() + memset 0. ]

Signed-off-by: Martin Leisener <martin@leisener.de>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/lttng-events.c b/lttng-events.c
index 24a7b3ca9101464f774a4ec0cc5469d1224b96de..9769f89de2aa78bef23410cf1dce84fdaf0c4584 100644 (file)
--- a/lttng-events.c
+++ b/lttng-events.c
@@ -39,6 +39,7 @@
 #include "wrapper/file.h"
 #include <linux/jhash.h>
 #include <linux/uaccess.h>
+#include <linux/vmalloc.h>
 
 #include "wrapper/uuid.h"
 #include "wrapper/vmalloc.h"   /* for wrapper_vmalloc_sync_all() */
@@ -132,8 +133,7 @@ struct lttng_session *lttng_session_create(void)
                        GFP_KERNEL);
        if (!metadata_cache)
                goto err_free_session;
-       metadata_cache->data = kzalloc(METADATA_CACHE_DEFAULT_SIZE,
-                       GFP_KERNEL);
+       metadata_cache->data = vzalloc(METADATA_CACHE_DEFAULT_SIZE);
        if (!metadata_cache->data)
                goto err_free_cache;
        metadata_cache->cache_alloc = METADATA_CACHE_DEFAULT_SIZE;
@@ -163,7 +163,7 @@ void metadata_cache_destroy(struct kref *kref)
 {
        struct lttng_metadata_cache *cache =
                container_of(kref, struct lttng_metadata_cache, refcount);
-       kfree(cache->data);
+       vfree(cache->data);
        kfree(cache);
 }
 
@@ -1531,10 +1531,16 @@ int lttng_metadata_printf(struct lttng_session *session,
                tmp_cache_alloc_size = max_t(unsigned int,
                                session->metadata_cache->cache_alloc + len,
                                session->metadata_cache->cache_alloc << 1);
-               tmp_cache_realloc = krealloc(session->metadata_cache->data,
-                               tmp_cache_alloc_size, GFP_KERNEL);
+               tmp_cache_realloc = vzalloc(tmp_cache_alloc_size);
                if (!tmp_cache_realloc)
                        goto err;
+               if (session->metadata_cache->data) {
+                       memcpy(tmp_cache_realloc,
+                               session->metadata_cache->data,
+                               session->metadata_cache->cache_alloc);
+                       vfree(session->metadata_cache->data);
+               }
+
                session->metadata_cache->cache_alloc = tmp_cache_alloc_size;
                session->metadata_cache->data = tmp_cache_realloc;
        }