From 9bb237b6a670fa7a6af3adc65231b1f6fda44510 Mon Sep 17 00:00:00 2001 From: "Ed L. Cashin" Date: Fri, 8 Feb 2008 04:20:05 -0800 Subject: aoe: dynamically allocate a capped number of skbs when necessary What this Patch Does Even before this recent series of 12 patches to 2.6.22-rc4, the aoe driver was reusing a small set of skbs that were allocated once and were only used for outbound AoE commands. The network layer cannot be allowed to put_page on the data that is still associated with a bio we haven't returned to the block layer, so the aoe driver (even before the patch under discussion) is still the owner of skbs that have been handed to the network layer for transmission. We need to keep track of these skbs so that we can free them, but by tracking them, we can also easily re-use them. The new patch was a response to the behavior of certain network drivers. We cannot reuse an skb that the network driver still has in its transmit ring. Network drivers can defer transmit ring cleanup and then use the state in the skb to determine how many data segments to clean up in its transmit ring. The tg3 driver is one driver that behaves in this way. When the network driver defers cleanup of its transmit ring, the aoe driver can find itself in a situation where it would like to send an AoE command, and the AoE target is ready for more work, but the network driver still has all of the pre-allocated skbs. In that case, the new patch just calls alloc_skb, as you'd expect. We don't want to get carried away, though. We try not to do excessive allocation in the write path, so we cap the number of skbs we dynamically allocate. Probably calling it a "dynamic pool" is misleading. We were already trying to use a small fixed-size set of pre-allocated skbs before this patch, and this patch just provides a little headroom (with a ceiling, though) to accomodate network drivers that hang onto skbs, by allocating when needed. The d->skbpool_hd list of allocated skbs is necessary so that we can free them later. We didn't notice the need for this headroom until AoE targets got fast enough. Alternatives If the network layer never did a put_page on the pages in the bio's we get from the block layer, then it would be possible for us to hand skbs to the network layer and forget about them, allowing the network layer to free skbs itself (and thereby calling our own skb->destructor callback function if we needed that). In that case we could get rid of the pre-allocated skbs and also the d->skbpool_hd, instead just calling alloc_skb every time we wanted to transmit a packet. The slab allocator would effectively maintain the list of skbs. Besides a loss of CPU cache locality, the main concern with that approach the danger that it would increase the likelihood of deadlock when VM is trying to free pages by writing dirty data from the page cache through the aoe driver out to persistent storage on an AoE device. Right now we have a situation where we have pre-allocation that corresponds to how much we use, which seems ideal. Of course, there's still the separate issue of receiving the packets that tell us that a write has successfully completed on the AoE target. When memory is low and VM is using AoE to flush dirty data to free up pages, it would be perfect if there were a way for us to register a fast callback that could recognize write command completion responses. But I don't think the current problems with the receive side of the situation are a justification for exacerbating the problem on the transmit side. Signed-off-by: Ed L. Cashin Cc: Greg KH Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/block/aoe/aoecmd.c | 117 ++++++++++++++++++++++++++++++++------------- 1 file changed, 83 insertions(+), 34 deletions(-) (limited to 'drivers/block/aoe/aoecmd.c') diff --git a/drivers/block/aoe/aoecmd.c b/drivers/block/aoe/aoecmd.c index 1be5150bcd3b..b49e06ef121e 100644 --- a/drivers/block/aoe/aoecmd.c +++ b/drivers/block/aoe/aoecmd.c @@ -106,45 +106,104 @@ ifrotate(struct aoetgt *t) } } +static void +skb_pool_put(struct aoedev *d, struct sk_buff *skb) +{ + if (!d->skbpool_hd) + d->skbpool_hd = skb; + else + d->skbpool_tl->next = skb; + d->skbpool_tl = skb; +} + +static struct sk_buff * +skb_pool_get(struct aoedev *d) +{ + struct sk_buff *skb; + + skb = d->skbpool_hd; + if (skb && atomic_read(&skb_shinfo(skb)->dataref) == 1) { + d->skbpool_hd = skb->next; + skb->next = NULL; + return skb; + } + if (d->nskbpool < NSKBPOOLMAX + && (skb = new_skb(ETH_ZLEN))) { + d->nskbpool++; + return skb; + } + return NULL; +} + +/* freeframe is where we do our load balancing so it's a little hairy. */ static struct frame * freeframe(struct aoedev *d) { - struct frame *f, *e; + struct frame *f, *e, *rf; struct aoetgt **t; - ulong n; + struct sk_buff *skb; if (d->targets[0] == NULL) { /* shouldn't happen, but I'm paranoid */ printk(KERN_ERR "aoe: NULL TARGETS!\n"); return NULL; } - t = d->targets; - do { - if (t != d->htgt - && (*t)->ifp->nd - && (*t)->nout < (*t)->maxout) { - n = (*t)->nframes; + t = d->tgt; + t++; + if (t >= &d->targets[NTARGETS] || !*t) + t = d->targets; + for (;;) { + if ((*t)->nout < (*t)->maxout + && t != d->htgt + && (*t)->ifp->nd) { + rf = NULL; f = (*t)->frames; - e = f + n; + e = f + (*t)->nframes; for (; f < e; f++) { if (f->tag != FREETAG) continue; - if (atomic_read(&skb_shinfo(f->skb)->dataref) + skb = f->skb; + if (!skb + && !(f->skb = skb = new_skb(ETH_ZLEN))) + continue; + if (atomic_read(&skb_shinfo(skb)->dataref) != 1) { - n--; + if (!rf) + rf = f; continue; } - skb_shinfo(f->skb)->nr_frags = 0; - f->skb->data_len = 0; - skb_trim(f->skb, 0); +gotone: skb_shinfo(skb)->nr_frags = skb->data_len = 0; + skb_trim(skb, 0); d->tgt = t; ifrotate(*t); return f; } - if (n == 0) /* slow polling network card */ + /* Work can be done, but the network layer is + holding our precious packets. Try to grab + one from the pool. */ + f = rf; + if (f == NULL) { /* more paranoia */ + printk(KERN_ERR + "aoe: freeframe: %s.\n", + "unexpected null rf"); + d->flags |= DEVFL_KICKME; + return NULL; + } + skb = skb_pool_get(d); + if (skb) { + skb_pool_put(d, f->skb); + f->skb = skb; + goto gotone; + } + (*t)->dataref++; + if ((*t)->nout == 0) d->flags |= DEVFL_KICKME; } + if (t == d->tgt) /* we've looped and found nada */ + break; t++; - } while (t < &d->targets[NTARGETS] && *t); + if (t >= &d->targets[NTARGETS] || !*t) + t = d->targets; + } return NULL; } @@ -894,33 +953,23 @@ addtgt(struct aoedev *d, char *addr, ulong nframes) return NULL; t = kcalloc(1, sizeof *t, GFP_ATOMIC); + if (!t) + return NULL; f = kcalloc(nframes, sizeof *f, GFP_ATOMIC); - if (!t || !f) - goto bail; + if (!f) { + kfree(t); + return NULL; + } + t->nframes = nframes; t->frames = f; e = f + nframes; - for (; f < e; f++) { + for (; f < e; f++) f->tag = FREETAG; - f->skb = new_skb(ETH_ZLEN); - if (!f->skb) - break; - } - if (f != e) { - while (f > t->frames) { - f--; - dev_kfree_skb(f->skb); - } - goto bail; - } memcpy(t->addr, addr, sizeof t->addr); t->ifp = t->ifs; t->maxout = t->nframes; return *tt = t; -bail: - kfree(t); - kfree(f); - return NULL; } void -- cgit v1.2.3