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MINOR: pools/debug: slightly relax DEBUG_DONT_SHARE_POOLS 

The purpose of this debugging option was to prevent certain pools from
masking other ones when they were shared. For example, task, http_txn,
h2s, h1s, h1c, session, fcgi_strm, and connection are all 192 bytes and
would normally be mergedi, but not with this option. The problem is that
certain pools are declared multiple times with various parameters, which
are often very close, and due to the way the option works, they're not
shared either. Good examples of this are captures and stick tables. Some
configurations have large numbers of stick-tables of pretty similar types
and it's very common to end up with the following when the option is
enabled:

  $ socat - /tmp/sock1  <<< "show pools" | grep stick
    - Pool sticktables (160 bytes) : 0 allocated (0 bytes), 0 used, needed_avg 0, 0 failures, 1 users, @0x753800=56
    - Pool sticktables (160 bytes) : 0 allocated (0 bytes), 0 used, needed_avg 0, 0 failures, 1 users, @0x753880=57
    - Pool sticktables (160 bytes) : 0 allocated (0 bytes), 0 used, needed_avg 0, 0 failures, 1 users, @0x753900=58
    - Pool sticktables (160 bytes) : 0 allocated (0 bytes), 0 used, needed_avg 0, 0 failures, 1 users, @0x753980=59
    - Pool sticktables (160 bytes) : 0 allocated (0 bytes), 0 used, needed_avg 0, 0 failures, 1 users, @0x753a00=60
    - Pool sticktables (160 bytes) : 0 allocated (0 bytes), 0 used, needed_avg 0, 0 failures, 1 users, @0x753a80=61
    - Pool sticktables (160 bytes) : 0 allocated (0 bytes), 0 used, needed_avg 0, 0 failures, 1 users, @0x753b00=62
    - Pool sticktables (224 bytes) : 0 allocated (0 bytes), 0 used, needed_avg 0, 0 failures, 1 users, @0x753780=55

In addition to not being convenient, it can have important effects on the
memory usage because these pools will not share their entries, so one stick
table cannot allocate from another one's pool.

This patch solves this by going back to the initial goal which was not to
have different pools in the same list. Instead of masking the MAP_F_SHARED
flag, it simply adds a test on the pool's name, and disables pool sharing
if the names differ. This way pools are not shared unless they're of the
same name and size, which doesn't hinder debugging. The same test above
now returns this:

  $ socat - /tmp/sock1  <<< "show pools" | grep stick
    - Pool sticktables (160 bytes) : 0 allocated (0 bytes), 0 used, needed_avg 0, 0 failures, 7 users, @0x3fadb30 [SHARED]
    - Pool sticktables (224 bytes) : 0 allocated (0 bytes), 0 used, needed_avg 0, 0 failures, 1 users, @0x3facaa0 [SHARED]

This is much better. This should probably be backported, in order to limit
the side effects of DEBUG_DONT_SHARE_POOLS being enabled in production.
This commit is contained in:
Willy Tarreau 2021-05-05 07:29:01 +02:00
parent 48129be18a
commit 1ab6c0bfd2
2 changed files with 5 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/haproxy/pool-t.h
View File

@ -50,14 +50,7 @@
#define CONFIG_HAP_NO_GLOBAL_POOLS
#endif
/* Pools of very similar size are shared by default, unless macro
* DEBUG_DONT_SHARE_POOLS is set.
*/
#ifndef DEBUG_DONT_SHARE_POOLS
#define MEM_F_SHARED 0x1
#else
#define MEM_F_SHARED 0
#endif
#define MEM_F_EXACT 0x2
/* By default, free objects are linked by a pointer stored at the beginning of

6
src/pool.c
View File

@ -80,7 +80,11 @@ struct pool_head *create_pool(char *name, unsigned int size, unsigned int flags)
* we look for a shareable one or for the next position
* before which we will insert a new one.
*/
if (flags & entry->flags & MEM_F_SHARED) {
if ((flags & entry->flags & MEM_F_SHARED)
#ifdef DEBUG_DONT_SHARE_POOLS
&& strcmp(name, entry->name) == 0
#endif
) {
/* we can share this one */
pool = entry;
DPRINTF(stderr, "Sharing %s with %s\n", name, pool->name);