[Xen-devel] [PATCH] libxl: remove freemem_slack

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

freemem_slack accounts for the amount of memory to be left free in the
system because empirical experiments seem to demonstrate that is needed
for "stability reasons".

As we don't have any actual data on these stability issues, remove it.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
CC: mlatimer@xxxxxxxx
CC: ian.campbell@xxxxxxxxxx
---
 tools/libxl/libxl.c |   59 ++++-----------------------------------------------
 1 file changed, 4 insertions(+), 55 deletions(-)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 9556a92..52a783a 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -4592,13 +4592,11 @@ static int libxl__fill_dom0_memory_info(libxl__gc *gc, 
uint32_t *target_memkb,
     int rc;
     libxl_dominfo info;
     libxl_physinfo physinfo;
-    char *target = NULL, *staticmax = NULL, *freememslack = NULL, *endptr = 
NULL;
+    char *target = NULL, *staticmax = NULL, *endptr = NULL;
     char *target_path = "/local/domain/0/memory/target";
     char *max_path = "/local/domain/0/memory/static-max";
-    char *free_mem_slack_path = "/local/domain/0/memory/freemem-slack";
     xs_transaction_t t;
     libxl_ctx *ctx = libxl__gc_owner(gc);
-    uint32_t free_mem_slack_kb = 0;
 
     libxl_dominfo_init(&info);
 
@@ -4607,8 +4605,7 @@ retry_transaction:
 
     target = libxl__xs_read(gc, t, target_path);
     staticmax = libxl__xs_read(gc, t, max_path);
-    freememslack = libxl__xs_read(gc, t, free_mem_slack_path);
-    if (target && staticmax && freememslack) {
+    if (target && staticmax) {
         rc = 0;
         goto out;
     }
@@ -4655,15 +4652,6 @@ retry_transaction:
         *max_memkb = (uint32_t) info.max_memkb;
     }
 
-    if (freememslack == NULL) {
-        free_mem_slack_kb = (uint32_t) (PAGE_TO_MEMKB(physinfo.total_pages) -
-                info.current_memkb);
-        /* From empirical measurements the free_mem_slack shouldn't be more
-         * than 15% of the total memory present on the system. */
-        if (free_mem_slack_kb > PAGE_TO_MEMKB(physinfo.total_pages) * 0.15)
-            free_mem_slack_kb = PAGE_TO_MEMKB(physinfo.total_pages) * 0.15;
-        libxl__xs_write(gc, t, free_mem_slack_path, "%"PRIu32, 
free_mem_slack_kb);
-    }
     rc = 0;
 
 out:
@@ -4678,33 +4666,6 @@ out:
     return rc;
 }
 
-/* returns how much memory should be left free in the system */
-static int libxl__get_free_memory_slack(libxl__gc *gc, uint32_t 
*free_mem_slack)
-{
-    int rc;
-    char *free_mem_slack_path = "/local/domain/0/memory/freemem-slack";
-    char *free_mem_slack_s, *endptr;
-    uint32_t target_memkb, max_memkb;
-
-retry:
-    free_mem_slack_s = libxl__xs_read(gc, XBT_NULL, free_mem_slack_path);
-    if (!free_mem_slack_s) {
-        rc = libxl__fill_dom0_memory_info(gc, &target_memkb, &max_memkb);
-        if (rc < 0)
-            return rc;
-        goto retry;
-    } else {
-        *free_mem_slack = strtoul(free_mem_slack_s, &endptr, 10);
-        if (*endptr != '\0') {
-            LIBXL__LOG_ERRNO(gc->owner, LIBXL__LOG_ERROR,
-                    "invalid free_mem_slack %s from %s\n",
-                    free_mem_slack_s, free_mem_slack_path);
-            return ERROR_FAIL;
-        }
-    }
-    return 0;
-}
-
 int libxl_set_memory_target(libxl_ctx *ctx, uint32_t domid,
         int32_t target_memkb, int relative, int enforce)
 {
@@ -4952,20 +4913,13 @@ int libxl_get_free_memory(libxl_ctx *ctx, uint32_t 
*memkb)
 {
     int rc = 0;
     libxl_physinfo info;
-    uint32_t freemem_slack;
     GC_INIT(ctx);
 
     rc = libxl_get_physinfo(ctx, &info);
     if (rc < 0)
         goto out;
-    rc = libxl__get_free_memory_slack(gc, &freemem_slack);
-    if (rc < 0)
-        goto out;
 
-    if ((info.free_pages + info.scrub_pages) * 4 > freemem_slack)
-        *memkb = (info.free_pages + info.scrub_pages) * 4 - freemem_slack;
-    else
-        *memkb = 0;
+    *memkb = (info.free_pages + info.scrub_pages) * 4;
 
 out:
     GC_FREE;
@@ -4977,18 +4931,13 @@ int libxl_wait_for_free_memory(libxl_ctx *ctx, uint32_t 
domid, uint32_t
 {
     int rc = 0;
     libxl_physinfo info;
-    uint32_t freemem_slack;
     GC_INIT(ctx);
 
-    rc = libxl__get_free_memory_slack(gc, &freemem_slack);
-    if (rc < 0)
-        goto out;
     while (wait_secs > 0) {
         rc = libxl_get_physinfo(ctx, &info);
         if (rc < 0)
             goto out;
-        if (info.free_pages * 4 >= freemem_slack &&
-            info.free_pages * 4 - freemem_slack >= memory_kb) {
+        if (info.free_pages * 4 >= memory_kb) {
             rc = 0;
             goto out;
         }
-- 
1.7.10.4


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel