Re: NFS client latencies

Ingo Molnar
2005-04-01T04:31:32Z

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* Lee Revell <rlrevell@joe-job.com> wrote:

> > > ah - cool! This was a 100 MB writeout so having 3.7 msecs to process
> > > 20K+ pages is not unreasonable. To break the latency, can i just do a
> > > simple lock-break, via the patch below?
> >
> > with this patch the worst-case latency during NFS writeout is down to 40
> > usecs (!).
> >
> > Lee: i've uploaded the -42-05 release with this patch included - could
> > you test it on your (no doubt more complex than mine) NFS setup?
>
> This fixes all the NFS related latency problems I was seeing. Now the
> longest latency from an NFS kernel compile with "make -j64" is 391
> usecs in get_swap_page.

great! The latest patches (-42-08 and later) have the reworked
nfs_scan_list() lock-breaker, which should perform similarly.

i bet these NFS patches also improve generic NFS performance on fast
networks. I've attached the full patchset with all fixes and
improvements included - might be worth a try in -mm?

Ingo

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--- linux/fs/nfs/inode.c.orig
+++ linux/fs/nfs/inode.c
@@ -118,7 +118,7 @@ nfs_write_inode(struct inode *inode, int
int flags = sync ? FLUSH_WAIT : 0;
int ret;

- ret = nfs_commit_inode(inode, 0, 0, flags);
+ ret = nfs_commit_inode(inode, flags);
if (ret < 0)
return ret;
return 0;
--- linux/fs/nfs/write.c.orig
+++ linux/fs/nfs/write.c
@@ -352,7 +352,7 @@ int nfs_writepages(struct address_space
if (err < 0)
goto out;
}
- err = nfs_commit_inode(inode, 0, 0, wb_priority(wbc));
+ err = nfs_commit_inode(inode, wb_priority(wbc));
if (err > 0) {
wbc->nr_to_write -= err;
err = 0;
@@ -446,6 +446,8 @@ nfs_mark_request_dirty(struct nfs_page *
struct nfs_inode *nfsi = NFS_I(inode);

spin_lock(&nfsi->req_lock);
+ radix_tree_tag_set(&nfsi->nfs_page_tree,
+ req->wb_index, NFS_PAGE_TAG_DIRTY);
nfs_list_add_request(req, &nfsi->dirty);
nfsi->ndirty++;
spin_unlock(&nfsi->req_lock);
@@ -503,13 +505,12 @@ nfs_wait_on_requests(struct inode *inode

spin_lock(&nfsi->req_lock);
next = idx_start;
- while (radix_tree_gang_lookup(&nfsi->nfs_page_tree, (void **)&req, next, 1)) {
+ while (radix_tree_gang_lookup_tag(&nfsi->nfs_page_tree, (void **)&req, next, 1, NFS_PAGE_TAG_WRITEBACK)) {
if (req->wb_index > idx_end)
break;

next = req->wb_index + 1;
- if (!NFS_WBACK_BUSY(req))
- continue;
+ BUG_ON(!NFS_WBACK_BUSY(req));

atomic_inc(&req->wb_count);
spin_unlock(&nfsi->req_lock);
@@ -538,12 +539,15 @@ static int
nfs_scan_dirty(struct inode *inode, struct list_head *dst, unsigned long idx_start, unsigned int npages)
{
struct nfs_inode *nfsi = NFS_I(inode);
- int res;
- res = nfs_scan_list(&nfsi->dirty, dst, idx_start, npages);
- nfsi->ndirty -= res;
- sub_page_state(nr_dirty,res);
- if ((nfsi->ndirty == 0) != list_empty(&nfsi->dirty))
- printk(KERN_ERR "NFS: desynchronized value of nfs_i.ndirty.\n");
+ int res = 0;
+
+ if (nfsi->ndirty != 0) {
+ res = nfs_scan_lock_dirty(nfsi, dst, idx_start, npages);
+ nfsi->ndirty -= res;
+ sub_page_state(nr_dirty,res);
+ if ((nfsi->ndirty == 0) != list_empty(&nfsi->dirty))
+ printk(KERN_ERR "NFS: desynchronized value of nfs_i.ndirty.\n");
+ }
return res;
}

@@ -562,11 +566,14 @@ static int
nfs_scan_commit(struct inode *inode, struct list_head *dst, unsigned long idx_start, unsigned int npages)
{
struct nfs_inode *nfsi = NFS_I(inode);
- int res;
- res = nfs_scan_list(&nfsi->commit, dst, idx_start, npages);
- nfsi->ncommit -= res;
- if ((nfsi->ncommit == 0) != list_empty(&nfsi->commit))
- printk(KERN_ERR "NFS: desynchronized value of nfs_i.ncommit.\n");
+ int res = 0;
+
+ if (nfsi->ncommit != 0) {
+ res = nfs_scan_list(nfsi, &nfsi->commit, dst, idx_start, npages);
+ nfsi->ncommit -= res;
+ if ((nfsi->ncommit == 0) != list_empty(&nfsi->commit))
+ printk(KERN_ERR "NFS: desynchronized value of nfs_i.ncommit.\n");
+ }
return res;
}
#endif
@@ -821,7 +828,7 @@ out:
#else
nfs_inode_remove_request(req);
#endif
- nfs_unlock_request(req);
+ nfs_clear_page_writeback(req);
}

static inline int flush_task_priority(int how)
@@ -952,7 +959,7 @@ out_bad:
nfs_writedata_free(data);
}
nfs_mark_request_dirty(req);
- nfs_unlock_request(req);
+ nfs_clear_page_writeback(req);
return -ENOMEM;
}

@@ -1002,7 +1009,7 @@ static int nfs_flush_one(struct list_hea
struct nfs_page *req = nfs_list_entry(head->next);
nfs_list_remove_request(req);
nfs_mark_request_dirty(req);
- nfs_unlock_request(req);
+ nfs_clear_page_writeback(req);
}
return -ENOMEM;
}
@@ -1029,7 +1036,7 @@ nfs_flush_list(struct list_head *head, i
req = nfs_list_entry(head->next);
nfs_list_remove_request(req);
nfs_mark_request_dirty(req);
- nfs_unlock_request(req);
+ nfs_clear_page_writeback(req);
}
return error;
}
@@ -1121,7 +1128,7 @@ static void nfs_writeback_done_full(stru
nfs_inode_remove_request(req);
#endif
next:
- nfs_unlock_request(req);
+ nfs_clear_page_writeback(req);
}
}

@@ -1210,36 +1217,24 @@ static void nfs_commit_rpcsetup(struct l
struct nfs_write_data *data, int how)
{
struct rpc_task *task = &data->task;
- struct nfs_page *first, *last;
+ struct nfs_page *first;
struct inode *inode;
- loff_t start, end, len;

/* Set up the RPC argument and reply structs
* NB: take care not to mess about with data->commit et al. */

list_splice_init(head, &data->pages);
first = nfs_list_entry(data->pages.next);
- last = nfs_list_entry(data->pages.prev);
inode = first->wb_context->dentry->d_inode;

- /*
- * Determine the offset range of requests in the COMMIT call.
- * We rely on the fact that data->pages is an ordered list...
- */
- start = req_offset(first);
- end = req_offset(last) + last->wb_bytes;
- len = end - start;
- /* If 'len' is not a 32-bit quantity, pass '0' in the COMMIT call */
- if (end >= i_size_read(inode) || len < 0 || len > (~((u32)0) >> 1))
- len = 0;
-
data->inode = inode;
data->cred = first->wb_context->cred;

data->args.fh = NFS_FH(data->inode);
- data->args.offset = start;
- data->args.count = len;
- data->res.count = len;
+ /* Note: we always request a commit of the entire inode */
+ data->args.offset = 0;
+ data->args.count = 0;
+ data->res.count = 0;
data->res.fattr = &data->fattr;
data->res.verf = &data->verf;

@@ -1278,7 +1273,7 @@ nfs_commit_list(struct list_head *head,
req = nfs_list_entry(head->next);
nfs_list_remove_request(req);
nfs_mark_request_commit(req);
- nfs_unlock_request(req);
+ nfs_clear_page_writeback(req);
}
return -ENOMEM;
}
@@ -1324,7 +1319,7 @@ nfs_commit_done(struct rpc_task *task)
dprintk(" mismatch\n");
nfs_mark_request_dirty(req);
next:
- nfs_unlock_request(req);
+ nfs_clear_page_writeback(req);
res++;
}
sub_page_state(nr_unstable,res);
@@ -1350,8 +1345,7 @@ static int nfs_flush_inode(struct inode
}

#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
-int nfs_commit_inode(struct inode *inode, unsigned long idx_start,
- unsigned int npages, int how)
+int nfs_commit_inode(struct inode *inode, int how)
{
struct nfs_inode *nfsi = NFS_I(inode);
LIST_HEAD(head);
@@ -1359,15 +1353,13 @@ int nfs_commit_inode(struct inode *inode
error = 0;

spin_lock(&nfsi->req_lock);
- res = nfs_scan_commit(inode, &head, idx_start, npages);
+ res = nfs_scan_commit(inode, &head, 0, 0);
+ spin_unlock(&nfsi->req_lock);
if (res) {
- res += nfs_scan_commit(inode, &head, 0, 0);
- spin_unlock(&nfsi->req_lock);
error = nfs_commit_list(&head, how);
- } else
- spin_unlock(&nfsi->req_lock);
- if (error < 0)
- return error;
+ if (error < 0)
+ return error;
+ }
return res;
}
#endif
@@ -1389,7 +1381,7 @@ int nfs_sync_inode(struct inode *inode,
error = nfs_flush_inode(inode, idx_start, npages, how);
#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
if (error == 0)
- error = nfs_commit_inode(inode, idx_start, npages, how);
+ error = nfs_commit_inode(inode, how);
#endif
} while (error > 0);
return error;
--- linux/fs/nfs/read.c.orig
+++ linux/fs/nfs/read.c
@@ -173,7 +173,6 @@ static int nfs_readpage_async(struct nfs
if (len < PAGE_CACHE_SIZE)
memclear_highpage_flush(page, len, PAGE_CACHE_SIZE - len);

- nfs_lock_request(new);
nfs_list_add_request(new, &one_request);
nfs_pagein_one(&one_request, inode);
return 0;
@@ -185,7 +184,6 @@ static void nfs_readpage_release(struct

nfs_clear_request(req);
nfs_release_request(req);
- nfs_unlock_request(req);

dprintk("NFS: read done (%s/%Ld %d@%Ld)\n",
req->wb_context->dentry->d_inode->i_sb->s_id,
@@ -553,7 +551,6 @@ readpage_async_filler(void *data, struct
}
if (len < PAGE_CACHE_SIZE)
memclear_highpage_flush(page, len, PAGE_CACHE_SIZE - len);
- nfs_lock_request(new);
nfs_list_add_request(new, desc->head);
return 0;
}
--- linux/fs/nfs/pagelist.c.orig
+++ linux/fs/nfs/pagelist.c
@@ -112,6 +112,33 @@ void nfs_unlock_request(struct nfs_page
}

/**
+ * nfs_set_page_writeback_locked - Lock a request for writeback
+ * @req:
+ */
+int nfs_set_page_writeback_locked(struct nfs_page *req)
+{
+ struct nfs_inode *nfsi = NFS_I(req->wb_context->dentry->d_inode);
+
+ if (!nfs_lock_request(req))
+ return 0;
+ radix_tree_tag_set(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_WRITEBACK);
+ return 1;
+}
+
+/**
+ * nfs_clear_page_writeback - Unlock request and wake up sleepers
+ */
+void nfs_clear_page_writeback(struct nfs_page *req)
+{
+ struct nfs_inode *nfsi = NFS_I(req->wb_context->dentry->d_inode);
+
+ spin_lock(&nfsi->req_lock);
+ radix_tree_tag_clear(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_WRITEBACK);
+ spin_unlock(&nfsi->req_lock);
+ nfs_unlock_request(req);
+}
+
+/**
* nfs_clear_request - Free up all resources allocated to the request
* @req:
*
@@ -151,36 +178,6 @@ nfs_release_request(struct nfs_page *req
}

/**
- * nfs_list_add_request - Insert a request into a sorted list
- * @req: request
- * @head: head of list into which to insert the request.
- *
- * Note that the wb_list is sorted by page index in order to facilitate
- * coalescing of requests.
- * We use an insertion sort that is optimized for the case of appended
- * writes.
- */
-void
-nfs_list_add_request(struct nfs_page *req, struct list_head *head)
-{
- struct list_head *pos;
-
-#ifdef NFS_PARANOIA
- if (!list_empty(&req->wb_list)) {
- printk(KERN_ERR "NFS: Add to list failed!\n");
- BUG();
- }
-#endif
- list_for_each_prev(pos, head) {
- struct nfs_page *p = nfs_list_entry(pos);
- if (p->wb_index < req->wb_index)
- break;
- }
- list_add(&req->wb_list, pos);
- req->wb_list_head = head;
-}
-
-/**
* nfs_wait_on_request - Wait for a request to complete.
* @req: request to wait upon.
*
@@ -243,6 +240,63 @@ nfs_coalesce_requests(struct list_head *
return npages;
}

+#define NFS_SCAN_MAXENTRIES 16
+/**
+ * nfs_scan_lock_dirty - Scan the radix tree for dirty requests
+ * @nfsi: NFS inode
+ * @dst: Destination list
+ * @idx_start: lower bound of page->index to scan
+ * @npages: idx_start + npages sets the upper bound to scan.
+ *
+ * Moves elements from one of the inode request lists.
+ * If the number of requests is set to 0, the entire address_space
+ * starting at index idx_start, is scanned.
+ * The requests are *not* checked to ensure that they form a contiguous set.
+ * You must be holding the inode's req_lock when calling this function
+ */
+int
+nfs_scan_lock_dirty(struct nfs_inode *nfsi, struct list_head *dst,
+ unsigned long idx_start, unsigned int npages)
+{
+ struct nfs_page *pgvec[NFS_SCAN_MAXENTRIES];
+ struct nfs_page *req;
+ unsigned long idx_end;
+ int found, i;
+ int res;
+
+ res = 0;
+ if (npages == 0)
+ idx_end = ~0;
+ else
+ idx_end = idx_start + npages - 1;
+
+ for (;;) {
+ found = radix_tree_gang_lookup_tag(&nfsi->nfs_page_tree,
+ (void **)&pgvec[0], idx_start, NFS_SCAN_MAXENTRIES,
+ NFS_PAGE_TAG_DIRTY);
+ if (found <= 0)
+ break;
+ for (i = 0; i < found; i++) {
+ req = pgvec[i];
+ if (req->wb_index > idx_end)
+ goto out;
+
+ idx_start = req->wb_index + 1;
+
+ if (nfs_set_page_writeback_locked(req)) {
+ radix_tree_tag_clear(&nfsi->nfs_page_tree,
+ req->wb_index, NFS_PAGE_TAG_DIRTY);
+ nfs_list_remove_request(req);
+ nfs_list_add_request(req, dst);
+ res++;
+ }
+ }
+ cond_resched_lock(&nfsi->req_lock);
+ }
+out:
+ return res;
+}
+
/**
* nfs_scan_list - Scan a list for matching requests
* @head: One of the NFS inode request lists
@@ -257,10 +311,12 @@ nfs_coalesce_requests(struct list_head *
* You must be holding the inode's req_lock when calling this function
*/
int
-nfs_scan_list(struct list_head *head, struct list_head *dst,
- unsigned long idx_start, unsigned int npages)
+nfs_scan_list(struct nfs_inode *nfsi, struct list_head *head,
+ struct list_head *dst, unsigned long idx_start,
+ unsigned int npages)
{
- struct list_head *pos, *tmp;
+ LIST_HEAD(locked);
+ struct list_head *pos;
struct nfs_page *req;
unsigned long idx_end;
int res;
@@ -271,21 +327,22 @@ nfs_scan_list(struct list_head *head, st
else
idx_end = idx_start + npages - 1;

- list_for_each_safe(pos, tmp, head) {
+ while (!list_empty(head)) {

+ pos = head->next;
req = nfs_list_entry(pos);

- if (req->wb_index < idx_start)
- continue;
- if (req->wb_index > idx_end)
- break;
-
- if (!nfs_lock_request(req))
- continue;
- nfs_list_remove_request(req);
- nfs_list_add_request(req, dst);
- res++;
+ if (!nfs_set_page_writeback_locked(req)) {
+ list_del(pos);
+ list_add(&req->wb_list, &locked);
+ } else {
+ nfs_list_remove_request(req);
+ nfs_list_add_request(req, dst);
+ res++;
+ }
+ cond_resched_lock(&nfsi->req_lock);
}
+ list_splice(&locked, head);
return res;
}

--- linux/include/linux/nfs_fs.h.orig
+++ linux/include/linux/nfs_fs.h
@@ -377,10 +377,10 @@ extern void nfs_commit_done(struct rpc_t
*/
extern int nfs_sync_inode(struct inode *, unsigned long, unsigned int, int);
#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
-extern int nfs_commit_inode(struct inode *, unsigned long, unsigned int, int);
+extern int nfs_commit_inode(struct inode *, int);
#else
static inline int
-nfs_commit_inode(struct inode *inode, unsigned long idx_start, unsigned int npages, int how)
+nfs_commit_inode(struct inode *inode, int how)
{
return 0;
}
--- linux/include/linux/nfs_page.h.orig
+++ linux/include/linux/nfs_page.h
@@ -20,12 +20,19 @@
#include <asm/atomic.h>

/*
+ * Valid flags for the radix tree
+ */
+#define NFS_PAGE_TAG_DIRTY 0
+#define NFS_PAGE_TAG_WRITEBACK 1
+
+/*
* Valid flags for a dirty buffer
*/
#define PG_BUSY 0
#define PG_NEED_COMMIT 1
#define PG_NEED_RESCHED 2

+struct nfs_inode;
struct nfs_page {
struct list_head wb_list, /* Defines state of page: */
*wb_list_head; /* read/write/commit */
@@ -54,14 +61,17 @@ extern void nfs_clear_request(struct nfs
extern void nfs_release_request(struct nfs_page *req);

-extern void nfs_list_add_request(struct nfs_page *, struct list_head *);
-
-extern int nfs_scan_list(struct list_head *, struct list_head *,
- unsigned long, unsigned int);
+extern int nfs_scan_lock_dirty(struct nfs_inode *nfsi, struct list_head *dst,
+ unsigned long idx_start, unsigned int npages);
+extern int nfs_scan_list(struct nfs_inode *nfsi, struct list_head *,
+ struct list_head *, unsigned long, unsigned int);
extern int nfs_coalesce_requests(struct list_head *, struct list_head *,
unsigned int);
extern int nfs_wait_on_request(struct nfs_page *);
extern void nfs_unlock_request(struct nfs_page *req);
+extern int nfs_set_page_writeback_locked(struct nfs_page *req);
+extern void nfs_clear_page_writeback(struct nfs_page *req);
+

/*
* Lock the page of an asynchronous request without incrementing the wb_count
@@ -86,6 +96,18 @@ nfs_lock_request(struct nfs_page *req)
return 1;
}

+/**
+ * nfs_list_add_request - Insert a request into a list
+ * @req: request
+ * @head: head of list into which to insert the request.
+ */
+static inline void
+nfs_list_add_request(struct nfs_page *req, struct list_head *head)
+{
+ list_add_tail(&req->wb_list, head);
+ req->wb_list_head = head;
+}
+

/**
* nfs_list_remove_request - Remove a request from its wb_list
@@ -96,10 +118,6 @@ nfs_list_remove_request(struct nfs_page
{
if (list_empty(&req->wb_list))
return;
- if (!NFS_WBACK_BUSY(req)) {
- printk(KERN_ERR "NFS: unlocked request attempted removed from list!\n");
- BUG();
- }
list_del_init(&req->wb_list);
req->wb_list_head = NULL;
}