Commit fee852e3 authored by Steven Whitehouse's avatar Steven Whitehouse
Browse files

[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: default avatarSteven Whitehouse <swhiteho@redhat.com>
parent 330005c2

fs/gfs2/glock.c

+43 −23
Original line number Diff line number Diff line
@@ -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) {

fs/gfs2/incore.h

+1 −1
Original line number Diff line number Diff line
@@ -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;

};

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