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knfsd: nfsd4: vary maximum delegation limit based on RAM size 

Our original NFSv4 delegation policy was to give out a read delegation on any
open when it was possible to.

Since the lifetime of a delegation isn't limited to that of an open, a client
may quite reasonably hang on to a delegation as long as it has the inode
cached.  This becomes an obvious problem the first time a client's inode cache
approaches the size of the server's total memory.

Our first quick solution was to add a hard-coded limit.  This patch makes a
mild incremental improvement by varying that limit according to the server's
total memory size, allowing at most 4 delegations per megabyte of RAM.

My quick back-of-the-envelope calculation finds that in the worst case (where
every delegation is for a different inode), a delegation could take about
1.5K, which would make the worst case usage about 6% of memory.  The new limit
works out to be about the same as the old on a 1-gig server.

[akpm@linux-foundation.org: Don't needlessly bloat vmlinux]
[akpm@linux-foundation.org: Make it right for highmem machines]
Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Meelap Shah 2007-07-17 04:04:39 -07:00 committed by Linus Torvalds
parent 1e5140279f
commit c2f1a551de
3 changed files with 27 additions and 1 deletions
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26
fs/nfsd/nfs4state.c
View File

@ -49,6 +49,7 @@
#include <linux/nfsd/state.h>
#include <linux/nfsd/xdr4.h>
#include <linux/namei.h>
#include <linux/swap.h>
#include <linux/mutex.h>
#include <linux/lockd/bind.h>
#include <linux/module.h>
@ -150,6 +151,7 @@ get_nfs4_file(struct nfs4_file *fi)
}
static int num_delegations;
unsigned int max_delegations;
/*
* Open owner state (share locks)
@ -193,7 +195,7 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_stateid *stp, struct svc_f
struct nfs4_callback *cb = &stp->st_stateowner->so_client->cl_callback;
dprintk("NFSD alloc_init_deleg\n");
if (num_delegations > STATEID_HASH_SIZE * 4)
if (num_delegations > max_delegations)
return NULL;
dp = kmem_cache_alloc(deleg_slab, GFP_KERNEL);
if (dp == NULL)
@ -3197,6 +3199,27 @@ get_nfs4_grace_period(void)
return max(user_lease_time, lease_time) * HZ;
}
/*
* Since the lifetime of a delegation isn't limited to that of an open, a
* client may quite reasonably hang on to a delegation as long as it has
* the inode cached. This becomes an obvious problem the first time a
* client's inode cache approaches the size of the server's total memory.
*
* For now we avoid this problem by imposing a hard limit on the number
* of delegations, which varies according to the server's memory size.
*/
static void
set_max_delegations(void)
{
/*
* Allow at most 4 delegations per megabyte of RAM. Quick
* estimates suggest that in the worst case (where every delegation
* is for a different inode), a delegation could take about 1.5K,
* giving a worst case usage of about 6% of memory.
*/
max_delegations = nr_free_buffer_pages() >> (20 - 2 - PAGE_SHIFT);
}
/* initialization to perform when the nfsd service is started: */
static void
@ -3212,6 +3235,7 @@ __nfs4_state_start(void)
grace_time/HZ);
laundry_wq = create_singlethread_workqueue("nfsd4");
queue_delayed_work(laundry_wq, &laundromat_work, grace_time);
set_max_delegations();
}
int

1
include/linux/nfsd/nfsd.h
View File

@ -148,6 +148,7 @@ extern int nfsd_max_blksize;
* NFSv4 State
*/
#ifdef CONFIG_NFSD_V4
extern unsigned int max_delegations;
void nfs4_state_init(void);
int nfs4_state_start(void);
void nfs4_state_shutdown(void);

1
mm/page_alloc.c
View File

@ -1484,6 +1484,7 @@ unsigned int nr_free_buffer_pages(void)
{
return nr_free_zone_pages(gfp_zone(GFP_USER));
}
EXPORT_SYMBOL_GPL(nr_free_buffer_pages);
/*
* Amount of free RAM allocatable within all zones