Re: [PATCH 5/5] nfsd41: replace page based DRC with buffer based DRC

J. Bruce Fields
2009-08-28T21:33:22Z

On Thu, Aug 27, 2009 at 12:07:44PM -0400, andros@netapp.com wrote:
> From: Andy Adamson <andros@netapp.com>
>
> Use NFSD_SLOT_CACHE_SIZE size buffers for sessions DRC instead of holding nfsd
> pages in cache.
>
> Connectathon testing has shown that 1024 bytes for encoded compound operation
> responses past the sequence operation is sufficient, 512 bytes is a little too
> small. Set NFSD_SLOT_CACHE_SIZE to 1024.
>
> Allocate memory for the session DRC in the CREATE_SESSION operation
> to guarantee that the memory resource is available for caching responses.
> Allocate each slot individually in preparation for slot table size negotiation.
>
> Remove struct nfsd4_cache_entry and helper functions for the old page-based
> DRC.
>
> The iov_len calculation in nfs4svc_encode_compoundres is now always
> correct, clean up the nfs4svc_encode_compoundres session logic.
>
> The nfsd4_compound_state statp pointer is also not used.
> Remove nfsd4_set_statp().
>
> Move useful nfsd4_cache_entry fields into nfsd4_slot.
>
> Signed-off-by: Andy Adamson <andros@netapp.com
> ---
> fs/nfsd/nfs4state.c | 207 ++++++++++++--------------------------------
> fs/nfsd/nfs4xdr.c | 13 ++--
> fs/nfsd/nfssvc.c | 4 -
> include/linux/nfsd/state.h | 27 ++----
> include/linux/nfsd/xdr4.h | 5 +-
> 5 files changed, 74 insertions(+), 182 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 4695cec..2d72d5c 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -510,12 +510,22 @@ static int init_forechannel_attrs(struct svc_rqst *rqstp,
> return status;
> }
>
> +static void
> +free_session_slots(struct nfsd4_session *ses)
> +{
> + int i;
> +
> + for (i = 0; i < ses->se_fchannel.maxreqs; i++)
> + kfree(ses->se_slots[i]);
> +}
> +
> static int
> alloc_init_session(struct svc_rqst *rqstp, struct nfs4_client *clp,
> struct nfsd4_create_session *cses)
> {
> struct nfsd4_session *new, tmp;
> - int idx, status = nfserr_serverfault, slotsize;
> + struct nfsd4_slot *sp;
> + int idx, status = nfserr_serverfault, slotsize, cachesize, i;

Just as a style thing: that list's getting a little long. Could you
keep at least "status" on a separate line?

>
> memset(&tmp, 0, sizeof(tmp));
>
> @@ -526,14 +536,23 @@ alloc_init_session(struct svc_rqst *rqstp, struct nfs4_client *clp,
> if (status)
> goto out;
>
> - /* allocate struct nfsd4_session and slot table in one piece */
> - slotsize = tmp.se_fchannel.maxreqs * sizeof(struct nfsd4_slot);
> + /* allocate struct nfsd4_session and slot table pointers in one piece */
> + slotsize = tmp.se_fchannel.maxreqs * sizeof(struct nfsd4_slot *);
> new = kzalloc(sizeof(*new) + slotsize, GFP_KERNEL);

I think this is OK for now, but maybe stick something like:

BUILD_BUG_ON(NFSD_MAX_SLOTS_PER_SESSION * sizeof(struct nfsd4_slot)
+ sizeof(struct nfsd4_session) > PAGE_SIZE);

in state.h just to warn anyone who wants to blindly bump up
NFSD_MAX_SLOTS_PER_SESSION. (It's not really forbidden to kmalloc more
than a page, but it's also not reliable, and if it becomes necessary
then we'd rather find some way to code around it.)

> if (!new)
> goto out;
>
> memcpy(new, &tmp, sizeof(*new));
>
> + /* allocate each struct nfsd4_slot and data cache in one piece */
> + cachesize = new->se_fchannel.maxresp_cached - NFSD_MIN_HDR_SEQ_SZ;
> + for (i = 0; i < new->se_fchannel.maxreqs; i++) {
> + sp = kzalloc(sizeof(*sp) + cachesize, GFP_KERNEL);
> + if (!sp)
> + goto out_free;
> + new->se_slots[i] = sp;
> + }
> +
> new->se_client = clp;
> gen_sessionid(new);
> idx = hash_sessionid(&new->se_sessionid);
> @@ -550,6 +569,10 @@ alloc_init_session(struct svc_rqst *rqstp, struct nfs4_client *clp,
> status = nfs_ok;
> out:
> return status;
> +out_free:
> + free_session_slots(new);
> + kfree(new);
> + goto out;
> }
>
> /* caller must hold sessionid_lock */
> @@ -592,22 +615,16 @@ release_session(struct nfsd4_session *ses)
> nfsd4_put_session(ses);
> }
>
> -static void nfsd4_release_respages(struct page **respages, short resused);
> -
> void
> free_session(struct kref *kref)
> {
> struct nfsd4_session *ses;
> - int i;
>
> ses = container_of(kref, struct nfsd4_session, se_ref);
> - for (i = 0; i < ses->se_fchannel.maxreqs; i++) {
> - struct nfsd4_cache_entry *e = &ses->se_slots[i].sl_cache_entry;
> - nfsd4_release_respages(e->ce_respages, e->ce_resused);
> - }
> spin_lock(&nfsd_drc_lock);
> nfsd_drc_mem_used -= ses->se_fchannel.maxreqs * NFSD_SLOT_CACHE_SIZE;
> spin_unlock(&nfsd_drc_lock);
> + free_session_slots(ses);
> kfree(ses);
> }
>
> @@ -964,116 +981,32 @@ out_err:
> return;
> }
>
> -void
> -nfsd4_set_statp(struct svc_rqst *rqstp, __be32 *statp)
> -{
> - struct nfsd4_compoundres *resp = rqstp->rq_resp;
> -
> - resp->cstate.statp = statp;
> -}
> -
> -/*
> - * Dereference the result pages.
> - */
> -static void
> -nfsd4_release_respages(struct page **respages, short resused)
> -{
> - int i;
> -
> - dprintk("--> %s\n", __func__);
> - for (i = 0; i < resused; i++) {
> - if (!respages[i])
> - continue;
> - put_page(respages[i]);
> - respages[i] = NULL;
> - }
> -}
> -
> -static void
> -nfsd4_copy_pages(struct page **topages, struct page **frompages, short count)
> -{
> - int i;
> -
> - for (i = 0; i < count; i++) {
> - topages[i] = frompages[i];
> - if (!topages[i])
> - continue;
> - get_page(topages[i]);
> - }
> -}
> -
> /*
> - * Cache the reply pages up to NFSD_PAGES_PER_SLOT + 1, clearing the previous
> - * pages. We add a page to NFSD_PAGES_PER_SLOT for the case where the total
> - * length of the XDR response is less than se_fmaxresp_cached
> - * (NFSD_PAGES_PER_SLOT * PAGE_SIZE) but the xdr_buf pages is used for a
> - * of the reply (e.g. readdir).
> - *
> - * Store the base and length of the rq_req.head[0] page
> - * of the NFSv4.1 data, just past the rpc header.
> + * Cache a reply. nfsd4_check_drc_limit() has bounded the cache size.
> */
> void
> nfsd4_store_cache_entry(struct nfsd4_compoundres *resp)
> {
> - struct nfsd4_cache_entry *entry = &resp->cstate.slot->sl_cache_entry;
> - struct svc_rqst *rqstp = resp->rqstp;
> - struct kvec *resv = &rqstp->rq_res.head[0];
> -
> - dprintk("--> %s entry %p\n", __func__, entry);
> + struct nfsd4_slot *slot = resp->cstate.slot;
> + unsigned int base;
>
> - nfsd4_release_respages(entry->ce_respages, entry->ce_resused);
> - entry->ce_opcnt = resp->opcnt;
> - entry->ce_status = resp->cstate.status;
> + dprintk("--> %s slot %p\n", __func__, slot);
>
> - /*
> - * Don't need a page to cache just the sequence operation - the slot
> - * does this for us!
> - */
> + slot->sl_opcnt = resp->opcnt;
> + slot->sl_status = resp->cstate.status;
>
> if (nfsd4_not_cached(resp)) {
> - entry->ce_resused = 0;
> - entry->ce_rpchdrlen = 0;
> - dprintk("%s Just cache SEQUENCE. ce_cachethis %d\n", __func__,
> - resp->cstate.slot->sl_cache_entry.ce_cachethis);
> + slot->sl_datalen = 0;
> return;
> }
> - entry->ce_resused = rqstp->rq_resused;
> - if (entry->ce_resused > NFSD_PAGES_PER_SLOT + 1)
> - entry->ce_resused = NFSD_PAGES_PER_SLOT + 1;
> - nfsd4_copy_pages(entry->ce_respages, rqstp->rq_respages,
> - entry->ce_resused);
> - entry->ce_datav.iov_base = resp->cstate.statp;
> - entry->ce_datav.iov_len = resv->iov_len - ((char *)resp->cstate.statp -
> - (char *)page_address(rqstp->rq_respages[0]));
> - /* Current request rpc header length*/
> - entry->ce_rpchdrlen = (char *)resp->cstate.statp -
> - (char *)page_address(rqstp->rq_respages[0]);
> -}
> -
> -/*
> - * We keep the rpc header, but take the nfs reply from the replycache.
> - */
> -static int
> -nfsd41_copy_replay_data(struct nfsd4_compoundres *resp,
> - struct nfsd4_cache_entry *entry)
> -{
> - struct svc_rqst *rqstp = resp->rqstp;
> - struct kvec *resv = &resp->rqstp->rq_res.head[0];
> - int len;
> -
> - /* Current request rpc header length*/
> - len = (char *)resp->cstate.statp -
> - (char *)page_address(rqstp->rq_respages[0]);
> - if (entry->ce_datav.iov_len + len > PAGE_SIZE) {
> - dprintk("%s v41 cached reply too large (%Zd).\n", __func__,
> - entry->ce_datav.iov_len);
> - return 0;
> - }
> - /* copy the cached reply nfsd data past the current rpc header */
> - memcpy((char *)resv->iov_base + len, entry->ce_datav.iov_base,
> - entry->ce_datav.iov_len);
> - resv->iov_len = len + entry->ce_datav.iov_len;
> - return 1;
> + slot->sl_datalen = (char *)resp->p - (char *)resp->cstate.datap;
> + base = (char *)resp->cstate.datap -
> + (char *)resp->xbuf->head[0].iov_base;
> + if (read_bytes_from_xdr_buf(resp->xbuf, base, slot->sl_data,
> + slot->sl_datalen))
> + printk(KERN_WARNING
> + "nfsd: sessions DRC could not cache compound\n");

I'd make this WARN("nfsd:...") just to make it completely clear it's a
kernel bug. (This case should be caught by nfsd4_check_drc_limit unless
we've messed something up, right?)

> + return;
> }
>
> /*
> @@ -1091,14 +1024,14 @@ nfsd4_enc_sequence_replay(struct nfsd4_compoundargs *args,
> struct nfsd4_slot *slot = resp->cstate.slot;
>
> dprintk("--> %s resp->opcnt %d cachethis %u \n", __func__,
> - resp->opcnt, resp->cstate.slot->sl_cache_entry.ce_cachethis);
> + resp->opcnt, resp->cstate.slot->sl_cachethis);
>
> /* Encode the replayed sequence operation */
> op = &args->ops[resp->opcnt - 1];
> nfsd4_encode_operation(resp, op);
>
> /* Return nfserr_retry_uncached_rep in next operation. */
> - if (args->opcnt > 1 && slot->sl_cache_entry.ce_cachethis == 0) {
> + if (args->opcnt > 1 && slot->sl_cachethis == 0) {
> op = &args->ops[resp->opcnt++];
> op->status = nfserr_retry_uncached_rep;
> nfsd4_encode_operation(resp, op);
> @@ -1107,57 +1040,29 @@ nfsd4_enc_sequence_replay(struct nfsd4_compoundargs *args,
> }
>
> /*
> - * Keep the first page of the replay. Copy the NFSv4.1 data from the first
> - * cached page. Replace any futher replay pages from the cache.
> + * The sequence operation is not cached because we can use the slot and
> + * session values.
> */
> __be32
> nfsd4_replay_cache_entry(struct nfsd4_compoundres *resp,
> struct nfsd4_sequence *seq)
> {
> - struct nfsd4_cache_entry *entry = &resp->cstate.slot->sl_cache_entry;
> + struct nfsd4_slot *slot = resp->cstate.slot;
> __be32 status;
>
> - dprintk("--> %s entry %p\n", __func__, entry);
> -
> - /*
> - * If this is just the sequence operation, we did not keep
> - * a page in the cache entry because we can just use the
> - * slot info stored in struct nfsd4_sequence that was checked
> - * against the slot in nfsd4_sequence().
> - *
> - * This occurs when seq->cachethis is FALSE, or when the client
> - * session inactivity timer fires and a solo sequence operation
> - * is sent (lease renewal).
> - */
> + dprintk("--> %s slot %p\n", __func__, slot);
>
> /* Either returns 0 or nfserr_retry_uncached */
> status = nfsd4_enc_sequence_replay(resp->rqstp->rq_argp, resp);
> if (status == nfserr_retry_uncached_rep)
> return status;
>
> - if (!nfsd41_copy_replay_data(resp, entry)) {
> - /*
> - * Not enough room to use the replay rpc header, send the
> - * cached header. Release all the allocated result pages.
> - */
> - svc_free_res_pages(resp->rqstp);
> - nfsd4_copy_pages(resp->rqstp->rq_respages, entry->ce_respages,
> - entry->ce_resused);
> - } else {
> - /* Release all but the first allocated result page */
> -
> - resp->rqstp->rq_resused--;
> - svc_free_res_pages(resp->rqstp);
> -
> - nfsd4_copy_pages(&resp->rqstp->rq_respages[1],
> - &entry->ce_respages[1],
> - entry->ce_resused - 1);
> - }
> + /* The sequence operation has been encoded, cstate->datap set. */
> + memcpy(resp->cstate.datap, slot->sl_data, slot->sl_datalen);
>
> - resp->rqstp->rq_resused = entry->ce_resused;
> - resp->opcnt = entry->ce_opcnt;
> - resp->cstate.iovlen = entry->ce_datav.iov_len + entry->ce_rpchdrlen;
> - status = entry->ce_status;
> + resp->opcnt = slot->sl_opcnt;
> + resp->p = resp->cstate.datap + XDR_QUADLEN(slot->sl_datalen);
> + status = slot->sl_status;
>
> return status;
> }
> @@ -1489,7 +1394,7 @@ nfsd4_sequence(struct svc_rqst *rqstp,
> if (seq->slotid >= session->se_fchannel.maxreqs)
> goto out;
>
> - slot = &session->se_slots[seq->slotid];
> + slot = session->se_slots[seq->slotid];
> dprintk("%s: slotid %d\n", __func__, seq->slotid);
>
> /* We do not negotiate the number of slots yet, so set the
> @@ -1502,7 +1407,7 @@ nfsd4_sequence(struct svc_rqst *rqstp,
> cstate->slot = slot;
> cstate->session = session;
> /* Return the cached reply status and set cstate->status
> - * for nfsd4_svc_encode_compoundres processing */
> + * for nfsd4_proc_compound processing */
> status = nfsd4_replay_cache_entry(resp, seq);
> cstate->status = nfserr_replay_cache;
> goto replay_cache;
> @@ -1513,7 +1418,7 @@ nfsd4_sequence(struct svc_rqst *rqstp,
> /* Success! bump slot seqid */
> slot->sl_inuse = true;
> slot->sl_seqid = seq->seqid;
> - slot->sl_cache_entry.ce_cachethis = seq->cachethis;
> + slot->sl_cachethis = seq->cachethis;
>
> cstate->slot = slot;
> cstate->session = session;
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index fdf632b..49824ea 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -3064,6 +3064,7 @@ nfsd4_encode_sequence(struct nfsd4_compoundres *resp, int nfserr,
> WRITE32(0);
>
> ADJUST_ARGS();
> + resp->cstate.datap = p; /* DRC cache data pointer */
> return 0;
> }
>
> @@ -3166,7 +3167,7 @@ static int nfsd4_check_drc_limit(struct nfsd4_compoundres *resp)
> return status;
>
> session = resp->cstate.session;
> - if (session == NULL || slot->sl_cache_entry.ce_cachethis == 0)
> + if (session == NULL || slot->sl_cachethis == 0)
> return status;
>
> if (resp->opcnt >= args->opcnt)
> @@ -3291,6 +3292,7 @@ nfs4svc_encode_compoundres(struct svc_rqst *rqstp, __be32 *p, struct nfsd4_compo
> /*
> * All that remains is to write the tag and operation count...
> */
> + struct nfsd4_compound_state *cs = &resp->cstate;
> struct kvec *iov;
> p = resp->tagp;
> *p++ = htonl(resp->taglen);
> @@ -3304,14 +3306,11 @@ nfs4svc_encode_compoundres(struct svc_rqst *rqstp, __be32 *p, struct nfsd4_compo
> iov = &rqstp->rq_res.head[0];
> iov->iov_len = ((char*)resp->p) - (char*)iov->iov_base;
> BUG_ON(iov->iov_len > PAGE_SIZE);
> - if (nfsd4_has_session(&resp->cstate)) {
> - if (resp->cstate.status == nfserr_replay_cache &&
> - !nfsd4_not_cached(resp)) {
> - iov->iov_len = resp->cstate.iovlen;
> - } else {
> + if (nfsd4_has_session(cs)) {
> + if (cs->status != nfserr_replay_cache) {
> nfsd4_store_cache_entry(resp);
> dprintk("%s: SET SLOT STATE TO AVAILABLE\n", __func__);
> - resp->cstate.slot->sl_inuse = 0;
> + resp->cstate.slot->sl_inuse = false;
> }
> nfsd4_put_session(resp->cstate.session);
> }
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index d68cd05..944ef01 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -576,10 +576,6 @@ nfsd_dispatch(struct svc_rqst *rqstp, __be32 *statp)
> + rqstp->rq_res.head[0].iov_len;
> rqstp->rq_res.head[0].iov_len += sizeof(__be32);
>
> - /* NFSv4.1 DRC requires statp */
> - if (rqstp->rq_vers == 4)
> - nfsd4_set_statp(rqstp, statp);
> -
> /* Now call the procedure handler, and encode NFS status. */
> nfserr = proc->pc_func(rqstp, rqstp->rq_argp, rqstp->rq_resp);
> nfserr = map_new_errors(rqstp->rq_vers, nfserr);
> diff --git a/include/linux/nfsd/state.h b/include/linux/nfsd/state.h
> index ff0b771..e745100 100644
> --- a/include/linux/nfsd/state.h
> +++ b/include/linux/nfsd/state.h
> @@ -94,30 +94,23 @@ struct nfs4_cb_conn {
>
> /* Maximum number of slots per session. 160 is useful for long haul TCP */
> #define NFSD_MAX_SLOTS_PER_SESSION 160
> -/* Maximum number of pages per slot cache entry */
> -#define NFSD_PAGES_PER_SLOT 1
> -#define NFSD_SLOT_CACHE_SIZE PAGE_SIZE
> /* Maximum number of operations per session compound */
> #define NFSD_MAX_OPS_PER_COMPOUND 16
> +/* Maximum session per slot cache size */
> +#define NFSD_SLOT_CACHE_SIZE 1024
> /* Maximum number of NFSD_SLOT_CACHE_SIZE slots per session */
> #define NFSD_CACHE_SIZE_SLOTS_PER_SESSION 32
> #define NFSD_MAX_MEM_PER_SESSION \
> (NFSD_CACHE_SIZE_SLOTS_PER_SESSION * NFSD_SLOT_CACHE_SIZE)
>
> -struct nfsd4_cache_entry {
> - __be32 ce_status;
> - struct kvec ce_datav; /* encoded NFSv4.1 data in rq_res.head[0] */
> - struct page *ce_respages[NFSD_PAGES_PER_SLOT + 1];
> - int ce_cachethis;
> - short ce_resused;
> - int ce_opcnt;
> - int ce_rpchdrlen;
> -};
> -
> struct nfsd4_slot {
> - bool sl_inuse;
> - u32 sl_seqid;
> - struct nfsd4_cache_entry sl_cache_entry;
> + bool sl_inuse;
> + u32 sl_seqid;
> + int sl_cachethis;
> + int sl_opcnt;
> + __be32 sl_status;
> + u32 sl_datalen;
> + char sl_data[];

Could you just move sl_inuse to the end? It'll save a few bytes in the
structure (because the compiler will probably stick 3 bytes after it to
align sl_seqid.)

--b.

> };
>
> struct nfsd4_channel_attrs {
> @@ -159,7 +152,7 @@ struct nfsd4_session {
> struct nfs4_sessionid se_sessionid;
> struct nfsd4_channel_attrs se_fchannel;
> struct nfsd4_channel_attrs se_bchannel;
> - struct nfsd4_slot se_slots[]; /* forward channel slots */
> + struct nfsd4_slot *se_slots[]; /* forward channel slots */
> };
>
> static inline void
> diff --git a/include/linux/nfsd/xdr4.h b/include/linux/nfsd/xdr4.h
> index 3f71660..73164c2 100644
> --- a/include/linux/nfsd/xdr4.h
> +++ b/include/linux/nfsd/xdr4.h
> @@ -51,7 +51,7 @@ struct nfsd4_compound_state {
> /* For sessions DRC */
> struct nfsd4_session *session;
> struct nfsd4_slot *slot;
> - __be32 *statp;
> + __be32 *datap;
> size_t iovlen;
> u32 minorversion;
> u32 status;
> @@ -472,8 +472,7 @@ static inline bool nfsd4_is_solo_sequence(struct nfsd4_compoundres *resp)
>
> static inline bool nfsd4_not_cached(struct nfsd4_compoundres *resp)
> {
> - return !resp->cstate.slot->sl_cache_entry.ce_cachethis ||
> - nfsd4_is_solo_sequence(resp);
> + return !resp->cstate.slot->sl_cachethis || nfsd4_is_solo_sequence(resp);
> }
>
> #define NFS4_SVC_XDRSIZE sizeof(struct nfsd4_compoundargs)
> --
> 1.6.2.5
>