[GFS2] Shrink gfs2_inode memory by half

Here is something I spotted (while looking for something entirely
different) the other day.

Rather than using a completion in each and every struct gfs2_holder,
this removes it in favour of hashed wait queues, thus saving a
considerable amount of memory both on the stack (where a number of
gfs2_holder structures are allocated) and in particular in the
gfs2_inode which has 8 gfs2_holder structures embedded within it.

As a result on x86_64 the gfs2_inode shrinks from 2488 bytes to
1912 bytes, a saving of 576 bytes per inode (no thats not a typo!).
In actual practice we get a much better result than that since
now that a gfs2_inode is under the 2048 byte barrier, we get two
per 4k slab page effectively halving the amount of memory required
to store gfs2_inodes.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index fb1960b7fdde5be2c3dfe94b3cc21c7d8d1825ba..5341e03b873f6fb04d9f3912f773ea07111afb47 100644 (file)
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -19,6 +19,7 @@
 #include <linux/gfs2_ondisk.h>
 #include <linux/list.h>
 #include <linux/lm_interface.h>
+#include <linux/wait.h>
 #include <asm/uaccess.h>
 
 #include "gfs2.h"
@@ -395,7 +396,6 @@ void gfs2_holder_init(struct gfs2_glock *gl, unsigned int state, unsigned flags,
        gh->gh_flags = flags;
        gh->gh_error = 0;
        gh->gh_iflags = 0;
-       init_completion(&gh->gh_wait);
 
        if (gh->gh_state == LM_ST_EXCLUSIVE)
                gh->gh_flags |= GL_LOCAL_EXCL;
@@ -479,6 +479,29 @@ static void gfs2_holder_put(struct gfs2_holder *gh)
        kfree(gh);
 }
 
+static void gfs2_holder_dispose_or_wake(struct gfs2_holder *gh)
+{
+       if (test_bit(HIF_DEALLOC, &gh->gh_iflags)) {
+               gfs2_holder_put(gh);
+               return;
+       }
+       clear_bit(HIF_WAIT, &gh->gh_iflags);
+       smp_mb();
+       wake_up_bit(&gh->gh_iflags, HIF_WAIT);
+}
+
+static int holder_wait(void *word)
+{
+        schedule();
+        return 0;
+}
+
+static void wait_on_holder(struct gfs2_holder *gh)
+{
+       might_sleep();
+       wait_on_bit(&gh->gh_iflags, HIF_WAIT, holder_wait, TASK_UNINTERRUPTIBLE);
+}
+
 /**
  * rq_mutex - process a mutex request in the queue
  * @gh: the glock holder
@@ -493,7 +516,9 @@ static int rq_mutex(struct gfs2_holder *gh)
        list_del_init(&gh->gh_list);
        /*  gh->gh_error never examined.  */
        set_bit(GLF_LOCK, &gl->gl_flags);
-       complete(&gh->gh_wait);
+       clear_bit(HIF_WAIT, &gh->gh_flags);
+       smp_mb();
+       wake_up_bit(&gh->gh_iflags, HIF_WAIT);
 
        return 1;
 }
@@ -549,7 +574,7 @@ static int rq_promote(struct gfs2_holder *gh)
        gh->gh_error = 0;
        set_bit(HIF_HOLDER, &gh->gh_iflags);
 
-       complete(&gh->gh_wait);
+       gfs2_holder_dispose_or_wake(gh);
 
        return 0;
 }
@@ -573,10 +598,7 @@ static int rq_demote(struct gfs2_holder *gh)
                list_del_init(&gh->gh_list);
                gh->gh_error = 0;
                spin_unlock(&gl->gl_spin);
-               if (test_bit(HIF_DEALLOC, &gh->gh_iflags))
-                       gfs2_holder_put(gh);
-               else
-                       complete(&gh->gh_wait);
+               gfs2_holder_dispose_or_wake(gh);
                spin_lock(&gl->gl_spin);
        } else {
                gl->gl_req_gh = gh;
@@ -684,6 +706,8 @@ static void gfs2_glmutex_lock(struct gfs2_glock *gl)
 
        gfs2_holder_init(gl, 0, 0, &gh);
        set_bit(HIF_MUTEX, &gh.gh_iflags);
+       if (test_and_set_bit(HIF_WAIT, &gh.gh_iflags))
+               BUG();
 
        spin_lock(&gl->gl_spin);
        if (test_and_set_bit(GLF_LOCK, &gl->gl_flags)) {
@@ -691,11 +715,13 @@ static void gfs2_glmutex_lock(struct gfs2_glock *gl)
        } else {
                gl->gl_owner = current;
                gl->gl_ip = (unsigned long)__builtin_return_address(0);
-               complete(&gh.gh_wait);
+               clear_bit(HIF_WAIT, &gh.gh_iflags);
+               smp_mb();
+               wake_up_bit(&gh.gh_iflags, HIF_WAIT);
        }
        spin_unlock(&gl->gl_spin);
 
-       wait_for_completion(&gh.gh_wait);
+       wait_on_holder(&gh);
        gfs2_holder_uninit(&gh);
 }
 
@@ -774,6 +800,7 @@ restart:
                        return;
                set_bit(HIF_DEMOTE, &new_gh->gh_iflags);
                set_bit(HIF_DEALLOC, &new_gh->gh_iflags);
+               set_bit(HIF_WAIT, &new_gh->gh_iflags);
 
                goto restart;
        }
@@ -908,12 +935,8 @@ static void xmote_bh(struct gfs2_glock *gl, unsigned int ret)
 
        gfs2_glock_put(gl);
 
-       if (gh) {
-               if (test_bit(HIF_DEALLOC, &gh->gh_iflags))
-                       gfs2_holder_put(gh);
-               else
-                       complete(&gh->gh_wait);
-       }
+       if (gh)
+               gfs2_holder_dispose_or_wake(gh);
 }
 
 /**
@@ -999,12 +1022,8 @@ static void drop_bh(struct gfs2_glock *gl, unsigned int ret)
 
        gfs2_glock_put(gl);
 
-       if (gh) {
-               if (test_bit(HIF_DEALLOC, &gh->gh_iflags))
-                       gfs2_holder_put(gh);
-               else
-                       complete(&gh->gh_wait);
-       }
+       if (gh)
+               gfs2_holder_dispose_or_wake(gh);
 }
 
 /**
@@ -1105,8 +1124,7 @@ static int glock_wait_internal(struct gfs2_holder *gh)
        if (gh->gh_flags & LM_FLAG_PRIORITY)
                do_cancels(gh);
 
-       wait_for_completion(&gh->gh_wait);
-
+       wait_on_holder(gh);
        if (gh->gh_error)
                return gh->gh_error;
 
@@ -1162,6 +1180,8 @@ static void add_to_queue(struct gfs2_holder *gh)
        struct gfs2_holder *existing;
 
        BUG_ON(!gh->gh_owner);
+       if (test_and_set_bit(HIF_WAIT, &gh->gh_iflags))
+               BUG();
 
        existing = find_holder_by_owner(&gl->gl_holders, gh->gh_owner);
        if (existing) {

diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index 9114851ac53ee39b25aa8816b054989ec98b8ddc..a24c4af09ce08c61f0f7434cf643e67383b3619b 100644 (file)
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -128,6 +128,7 @@ enum {
        HIF_HOLDER              = 6,
        HIF_FIRST               = 7,
        HIF_ABORTED             = 9,
+       HIF_WAIT                = 10,
 };
 
 struct gfs2_holder {
@@ -140,7 +141,6 @@ struct gfs2_holder {
 
        int gh_error;
        unsigned long gh_iflags;
-       struct completion gh_wait;
        unsigned long gh_ip;
 };