From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38320) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dO2b7-0001JO-HA for qemu-devel@nongnu.org; Thu, 22 Jun 2017 09:56:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dO2b2-0005q9-TM for qemu-devel@nongnu.org; Thu, 22 Jun 2017 09:56:37 -0400 References: <20170613121639.17853-1-pbutsykin@virtuozzo.com> <20170613121639.17853-3-pbutsykin@virtuozzo.com> <364b26de-e7fa-1a90-ac33-2a444ca281eb@redhat.com> From: Pavel Butsykin Message-ID: Date: Thu, 22 Jun 2017 16:55:23 +0300 MIME-Version: 1.0 In-Reply-To: <364b26de-e7fa-1a90-ac33-2a444ca281eb@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2 2/4] qcow2: add qcow2_cache_discard List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Max Reitz , qemu-block@nongnu.org, qemu-devel@nongnu.org Cc: kwolf@redhat.com, eblake@redhat.com, armbru@redhat.com, den@openvz.org On 22.06.2017 01:29, Max Reitz wrote: > On 2017-06-13 14:16, Pavel Butsykin wrote: >> Whenever l2/refcount table clusters are discarded from the file we can >> automatically drop unnecessary content of the cache tables. This reduces >> the chance of eviction useful cache data and eliminates inconsistent data >> in thecache with the data in the file. >> >> Signed-off-by: Pavel Butsykin >> --- >> block/qcow2-cache.c | 21 +++++++++++++++++++++ >> block/qcow2-refcount.c | 5 +++++ >> block/qcow2.h | 1 + >> 3 files changed, 27 insertions(+) >> >> diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c >> index 1d25147392..7931edf237 100644 >> --- a/block/qcow2-cache.c >> +++ b/block/qcow2-cache.c >> @@ -411,3 +411,24 @@ void qcow2_cache_entry_mark_dirty(BlockDriverState *bs, Qcow2Cache *c, >> assert(c->entries[i].offset != 0); >> c->entries[i].dirty = true; >> } >> + >> +void qcow2_cache_discard(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset) >> +{ >> + int i; >> + >> + for (i = 0; i < c->size; i++) { >> + if (c->entries[i].offset == offset) { >> + goto found; /* table offset */ >> + } >> + } >> + return; >> + >> +found: >> + assert(c->entries[i].ref == 0); >> + >> + c->entries[i].offset = 0; >> + c->entries[i].lru_counter = 0; >> + c->entries[i].dirty = false; >> + >> + qcow2_cache_table_release(bs, c, i, 1); >> +} >> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c >> index 7c06061aae..576ab551d6 100644 >> --- a/block/qcow2-refcount.c >> +++ b/block/qcow2-refcount.c >> @@ -767,6 +767,11 @@ static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs, >> s->set_refcount(refcount_block, block_index, refcount); >> >> if (refcount == 0 && s->discard_passthrough[type]) { >> + qcow2_cache_put(bs, s->refcount_block_cache, &refcount_block); > > I don't like this very much. It works, but it feels bad. > > Would it be possible to store this refblock's offset somewhere and only > put it back if @offset is equal to that? > >> + qcow2_cache_discard(bs, s->refcount_block_cache, offset); >> + >> + qcow2_cache_discard(bs, s->l2_table_cache, offset); >> + > > So you're blindly calling qcow2_cache_discard() on @offset because > @offset may be pointing to a refblock or an L2 table? Right, that works, > but it still deserves a comment, I think (that we have no idea whether > @offset actually points to any of these refcount structures, but that we > also just don't have to care). > > Looks OK to me, functionally, but I'd at least like to have that comment. > Hmm.. We can split qcow2_cache_discard() and kill two birds with one stone. void* qcow2_cache_is_table_offset(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset) { int i; for (i = 0; i < c->size; i++) { if (c->entries[i].offset == offset) { return qcow2_cache_get_table_addr(bs, c, i); } } return NULL; } void qcow2_cache_discard(BlockDriverState *bs, Qcow2Cache *c, void table) { int i = qcow2_cache_get_table_idx(bs, c, table); assert(c->entries[i].ref == 0); c->entries[i].offset = 0; c->entries[i].lru_counter = 0; c->entries[i].dirty = false; qcow2_cache_table_release(bs, c, i, 1); } .... if (refcount == 0 && s->discard_passthrough[type]) { void *table; table = qcow2_cache_is_table_offset(bs, s->refcount_block_cache, offset); if (table != NULL) { qcow2_cache_put(bs, s->refcount_block_cache, &refcount_block); qcow2_cache_discard(bs, s->refcount_block_cache, table); } table = qcow2_cache_is_table_offset(bs, s->l2_table_cache, offset); if (table != NULL) { qcow2_cache_discard(bs, s->l2_table_cache, table); } ... > Max > >> update_refcount_discard(bs, cluster_offset, s->cluster_size); >> } >> } >> diff --git a/block/qcow2.h b/block/qcow2.h >> index 1801dc30dc..07faa6dc78 100644 >> --- a/block/qcow2.h >> +++ b/block/qcow2.h >> @@ -597,5 +597,6 @@ int qcow2_cache_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset, >> int qcow2_cache_get_empty(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset, >> void **table); >> void qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table); >> +void qcow2_cache_discard(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset); >> >> #endif >> > >