Commit c2f1a551dea8b37c2e0cb886885c250fb703e9d8

Authored by Meelap Shah
Committed by Linus Torvalds
1 parent 1e5140279f

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>

Showing 3 changed files with 27 additions and 1 deletions Side-by-side Diff

... ... @@ -49,6 +49,7 @@
49 49 #include <linux/nfsd/state.h>
50 50 #include <linux/nfsd/xdr4.h>
51 51 #include <linux/namei.h>
  52 +#include <linux/swap.h>
52 53 #include <linux/mutex.h>
53 54 #include <linux/lockd/bind.h>
54 55 #include <linux/module.h>
... ... @@ -150,6 +151,7 @@
150 151 }
151 152  
152 153 static int num_delegations;
  154 +unsigned int max_delegations;
153 155  
154 156 /*
155 157 * Open owner state (share locks)
... ... @@ -193,7 +195,7 @@
193 195 struct nfs4_callback *cb = &stp->st_stateowner->so_client->cl_callback;
194 196  
195 197 dprintk("NFSD alloc_init_deleg\n");
196   - if (num_delegations > STATEID_HASH_SIZE * 4)
  198 + if (num_delegations > max_delegations)
197 199 return NULL;
198 200 dp = kmem_cache_alloc(deleg_slab, GFP_KERNEL);
199 201 if (dp == NULL)
... ... @@ -3197,6 +3199,27 @@
3197 3199 return max(user_lease_time, lease_time) * HZ;
3198 3200 }
3199 3201  
  3202 +/*
  3203 + * Since the lifetime of a delegation isn't limited to that of an open, a
  3204 + * client may quite reasonably hang on to a delegation as long as it has
  3205 + * the inode cached. This becomes an obvious problem the first time a
  3206 + * client's inode cache approaches the size of the server's total memory.
  3207 + *
  3208 + * For now we avoid this problem by imposing a hard limit on the number
  3209 + * of delegations, which varies according to the server's memory size.
  3210 + */
  3211 +static void
  3212 +set_max_delegations(void)
  3213 +{
  3214 + /*
  3215 + * Allow at most 4 delegations per megabyte of RAM. Quick
  3216 + * estimates suggest that in the worst case (where every delegation
  3217 + * is for a different inode), a delegation could take about 1.5K,
  3218 + * giving a worst case usage of about 6% of memory.
  3219 + */
  3220 + max_delegations = nr_free_buffer_pages() >> (20 - 2 - PAGE_SHIFT);
  3221 +}
  3222 +
3200 3223 /* initialization to perform when the nfsd service is started: */
3201 3224  
3202 3225 static void
... ... @@ -3212,6 +3235,7 @@
3212 3235 grace_time/HZ);
3213 3236 laundry_wq = create_singlethread_workqueue("nfsd4");
3214 3237 queue_delayed_work(laundry_wq, &laundromat_work, grace_time);
  3238 + set_max_delegations();
3215 3239 }
3216 3240  
3217 3241 int
include/linux/nfsd/nfsd.h
... ... @@ -148,6 +148,7 @@
148 148 * NFSv4 State
149 149 */
150 150 #ifdef CONFIG_NFSD_V4
  151 +extern unsigned int max_delegations;
151 152 void nfs4_state_init(void);
152 153 int nfs4_state_start(void);
153 154 void nfs4_state_shutdown(void);
... ... @@ -1484,6 +1484,7 @@
1484 1484 {
1485 1485 return nr_free_zone_pages(gfp_zone(GFP_USER));
1486 1486 }
  1487 +EXPORT_SYMBOL_GPL(nr_free_buffer_pages);
1487 1488  
1488 1489 /*
1489 1490 * Amount of free RAM allocatable within all zones