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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:reply-to :from:date:message-id:subject:to:cc; bh=O7RI+ANZCHNvgYsg/bz6a/7oVysA3D5CTaFJ3UtCDDA=; b=kAyGj+2rCokZG/CEfXG1670vKS5IpSe0CrJZRCQKYWRU7MUKfbVSHoyTpgODSUdpGK gbPp+pUrF8CmKZvS7IDAwx4n6yHbo1JOJdBOE0Rs3iOAePseX0mIm3RqhV8LeBXcC+pu Z/uniPB/mkhb4B78wRk1hyy8f9GC90ZBmklIHQ0hqS9I63HnoiKbDsMjMu02PiOo6iQ5 dz0OnNkrsKHY4fiHSER641VYbJP1Dqnb1A8f/Igfe53t7RBtx5hf3S8V8ZUHYj12gPEw oPi0JxGD98zkkN7FwSEkRq+S7L9aF57/HQkSMsdBBOcO4VGhOYXorT+I4LozjAiAHdDx j3ng== X-Gm-Message-State: APjAAAWzllH7XFT2sBYGES4H6XBrAkTaBBusYQq7aoQcWaWvECj0FUDo YtYUu9SO5aEnAHIL6VZ/v8MZAOdQ/UeG5Ut6+59nlQ== X-Google-Smtp-Source: APXvYqy6eZ7MB/LTida1+Hif5ynLEAtu1BH0PdT2GENSQFHhWtDlOYEa/eVnCqsVADFPTTMy7lyxJQrwFGtmI6VCkME= X-Received: by 2002:a50:f05a:: with SMTP id u26mr82533525edl.116.1564145228041; Fri, 26 Jul 2019 05:47:08 -0700 (PDT) MIME-Version: 1.0 References: <20190723071342.383909-1-sgarzare@redhat.com> <20190725081334.s2btvq3zdorj7lb5@steredhat> <20190726084816.buweyjycku5qgl3o@steredhat> In-Reply-To: <20190726084816.buweyjycku5qgl3o@steredhat> From: Jason Dillaman Date: Fri, 26 Jul 2019 08:46:56 -0400 Message-ID: To: Stefano Garzarella Content-Type: text/plain; charset="UTF-8" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.85.208.65 Subject: Re: [Qemu-devel] [PATCH v3] block/rbd: add preallocation support X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: dillaman@redhat.com Cc: Kevin Wolf , qemu-block , Markus Armbruster , qemu-devel , Max Reitz , dillaman Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Jul 26, 2019 at 4:48 AM Stefano Garzarella wrote: > > On Thu, Jul 25, 2019 at 09:30:30AM -0400, Jason Dillaman wrote: > > On Thu, Jul 25, 2019 at 4:13 AM Stefano Garzarella wrote: > > > > > > On Wed, Jul 24, 2019 at 01:48:42PM -0400, Jason Dillaman wrote: > > > > On Tue, Jul 23, 2019 at 3:13 AM Stefano Garzarella wrote: > > > > > > > > > > This patch adds the support of preallocation (off/full) for the RBD > > > > > block driver. > > > > > If rbd_writesame() is available and supports zeroed buffers, we use > > > > > it to quickly fill the image when full preallocation is required. > > > > > > > > > > Signed-off-by: Stefano Garzarella > > > > > --- > > > > > v3: > > > > > - rebased on master > > > > > - filled with zeroed buffer [Max] > > > > > - used rbd_writesame() only when we can disable the discard of zeroed > > > > > buffers > > > > > - added 'since: 4.2' in qapi/block-core.json [Max] > > > > > - used buffer as large as the "stripe unit" > > > > > --- > > > > > block/rbd.c | 202 ++++++++++++++++++++++++++++++++++++++++--- > > > > > qapi/block-core.json | 5 +- > > > > > 2 files changed, 192 insertions(+), 15 deletions(-) > > > > > > > > > > diff --git a/block/rbd.c b/block/rbd.c > > > > > index 59757b3120..d923a5a26c 100644 > > > > > --- a/block/rbd.c > > > > > +++ b/block/rbd.c > > > > > @@ -64,6 +64,7 @@ > > > > > #define OBJ_MAX_SIZE (1UL << OBJ_DEFAULT_OBJ_ORDER) > > > > > > > > > > #define RBD_MAX_SNAPS 100 > > > > > +#define RBD_DEFAULT_CONCURRENT_OPS 10 > > > > > > > > > > /* The LIBRBD_SUPPORTS_IOVEC is defined in librbd.h */ > > > > > #ifdef LIBRBD_SUPPORTS_IOVEC > > > > > @@ -104,6 +105,7 @@ typedef struct BDRVRBDState { > > > > > char *image_name; > > > > > char *snap; > > > > > uint64_t image_size; > > > > > + bool ws_zero_supported; /* rbd_writesame() supports zeroed buffers */ > > > > > } BDRVRBDState; > > > > > > > > > > static int qemu_rbd_connect(rados_t *cluster, rados_ioctx_t *io_ctx, > > > > > @@ -333,6 +335,155 @@ static void qemu_rbd_memset(RADOSCB *rcb, int64_t offs) > > > > > } > > > > > } > > > > > > > > > > +static int qemu_rbd_get_max_concurrent_ops(rados_t cluster) > > > > > +{ > > > > > + char buf[16]; > > > > > + int ret, max_concurrent_ops; > > > > > + > > > > > + ret = rados_conf_get(cluster, "rbd_concurrent_management_ops", buf, > > > > > + sizeof(buf)); > > > > > + if (ret < 0) { > > > > > + return RBD_DEFAULT_CONCURRENT_OPS; > > > > > + } > > > > > + > > > > > + ret = qemu_strtoi(buf, NULL, 10, &max_concurrent_ops); > > > > > + if (ret < 0) { > > > > > + return RBD_DEFAULT_CONCURRENT_OPS; > > > > > + } > > > > > + > > > > > + return max_concurrent_ops; > > > > > +} > > > > > + > > > > > +static int qemu_rbd_do_truncate(rados_t cluster, rbd_image_t image, > > > > > + int64_t offset, PreallocMode prealloc, > > > > > + bool ws_zero_supported, Error **errp) > > > > > +{ > > > > > + uint64_t current_length; > > > > > + char *buf = NULL; > > > > > + int ret; > > > > > + > > > > > + ret = rbd_get_size(image, ¤t_length); > > > > > + if (ret < 0) { > > > > > + error_setg_errno(errp, -ret, "Failed to get file length"); > > > > > + goto out; > > > > > + } > > > > > + > > > > > + if (current_length > offset && prealloc != PREALLOC_MODE_OFF) { > > > > > + error_setg(errp, "Cannot use preallocation for shrinking files"); > > > > > + ret = -ENOTSUP; > > > > > + goto out; > > > > > + } > > > > > + > > > > > + switch (prealloc) { > > > > > + case PREALLOC_MODE_FULL: { > > > > > + uint64_t buf_size, current_offset = current_length; > > > > > + ssize_t bytes; > > > > > + > > > > > + ret = rbd_get_stripe_unit(image, &buf_size); > > > > > + if (ret < 0) { > > > > > + error_setg_errno(errp, -ret, "Failed to get stripe unit"); > > > > > + goto out; > > > > > + } > > > > > + > > > > > + ret = rbd_resize(image, offset); > > > > > + if (ret < 0) { > > > > > + error_setg_errno(errp, -ret, "Failed to resize file"); > > > > > + goto out; > > > > > + } > > > > > + > > > > > + buf = g_malloc0(buf_size); > > > > > + > > > > > +#ifdef LIBRBD_SUPPORTS_WRITESAME > > > > > + if (ws_zero_supported) { > > > > > + uint64_t writesame_max_size; > > > > > + int max_concurrent_ops; > > > > > + > > > > > + max_concurrent_ops = qemu_rbd_get_max_concurrent_ops(cluster); > > > > > + /* > > > > > + * We limit the rbd_writesame() size to avoid to spawn more then > > > > > + * 'rbd_concurrent_management_ops' concurrent operations. > > > > > + */ > > > > > + writesame_max_size = MIN(buf_size * max_concurrent_ops, INT_MAX); > > > > > > > > In the most efficient world, the 'buf_size' would be some small, fixed > > > > power of 2 value (like 512 bytes) since there isn't much need to send > > > > extra zeroes. You would then want to writesame the full stripe period > > > > (if possible), where a stripe period is the data block object size > > > > (defaults to 4MiB and is availble via 'rbd_stat') * the stripe count. > > > > In this case, the stripe count becomes the number of in-flight IOs. > > > > Therefore, you could substitute its value w/ the max_concurrent_ops to > > > > ensure you are issuing exactly max_concurrent_ops IOs per > > > > rbd_writesame call. > > > > > > > > > > Initially, I had a fixed buffer size to 4 KiB, but I noted that, when > > > we didn't use writesame, the rbd_write() was very slow, so I used the > > > stripe unit as a buffer size. > > > > > > Do you think is better to have a small buffer (512 byte) when we use > > > writesame or a 'stripe unit' buffer when we can't use it? > > > > I'd use a small buffer for rbd_writesame and then just reallocate the > > My idea was to allocate a small buffer for rbd_writesame and use the > same to write the remaining bytes that should be a few. > If the buffer was not allocated (so we didn't use the rbd_writesame), > I'll allocate the big one: > > if (ws_zero_supported) { > buf_size = 512; > buf = g_malloc0(buf_size); > ... > } > > if (!buf) { > buf_size = object_size * max_concurrent_ops; > buf = g_malloc0(buf_size); > } > > while (current_offset < offset) { > bytes = rbd_write(...) > ... > } > > > buffer to a larger size for "rbd_write". It would be most efficient to > > allocate a "object size * max concurrent ops" -sized buffer (up to > > Why "object size * max concurrent ops" and not > "stripe_unit * max concurrent ops"? > IIUC stripe_unit can be smaller than object size. Correct, stripe unit *must* be smaller than the object size (and both are powers of two). However, it's more efficient to send fewer larger writes to a backing object than sending more small writes -- especially in the case of writesame where you don't have the network overhead of transferring a large zeroed buffer. Replacing the full backing object is even more efficient since it will just need to perform a single backing disk allocation that will be continuous instead of fragmented. > > some reasonable maximum) for the standard rbd_write. Just make sure > > your "rbd_writes" offsets / length is aligned to the stripe period for > > the most efficient IO (i.e. the initial write might be smaller than > > the stripe period if the starting offset is unaligned). > > > > Okay, I'll do the first small write to align the next writes to the > stripe period (obj size * stripe_count). > > > > > > + > > > > > + while (offset - current_offset > buf_size) { > > > > > + bytes = MIN(offset - current_offset, writesame_max_size); > > > > > + /* > > > > > + * rbd_writesame() supports only request where the size of the > > > > > + * operation is multiple of buffer size. > > > > > + */ > > > > > + bytes -= bytes % buf_size; > > > > > + > > > > > + bytes = rbd_writesame(image, current_offset, bytes, buf, > > > > > + buf_size, 0); > > > > > > > > If the RBD in-memory cache is enabled during this operation, the > > > > writesame will effectively just be turned into a write. Therefore, > > > > when pre-allocating, you will want to disable the cache. > > > > > > > > > > During the creation, when preallocation is often used, we disable the cache: > > > > > > static int qemu_rbd_do_create(BlockdevCreateOptions *options, > > > const char *keypairs, const char *password_secret, > > > Error **errp) > > > { > > > ... > > > > > > ret = qemu_rbd_connect(&cluster, &io_ctx, opts->location, false, keypairs, > > > ^^ cache param > > > ... > > > } > > > > > > > > > Do you think I should disable it in any case during the preallocation? > > > > Assuming you can grow an image w/ full preallocation, I would > > definitely want to ensure that the cache is disabled since otherwise > > you would just be performing regular (non-offloaded) writes. > > > > Yes, make sense, I'll disable the cache. > > > > > > > > > > > > + if (bytes < 0) { > > > > > + ret = bytes; > > > > > + error_setg_errno(errp, -ret, > > > > > + "Failed to write for preallocation"); > > > > > + goto out; > > > > > + } > > > > > + > > > > > + current_offset += bytes; > > > > > + } > > > > > + } > > > > > +#endif /* LIBRBD_SUPPORTS_WRITESAME */ > > > > > + > > > > > + while (current_offset < offset) { > > > > > + bytes = rbd_write(image, current_offset, > > > > > + MIN(offset - current_offset, buf_size), buf); > > > > > + if (bytes < 0) { > > > > > + ret = bytes; > > > > > + error_setg_errno(errp, -ret, > > > > > + "Failed to write for preallocation"); > > > > > + goto out; > > > > > + } > > > > > + > > > > > + current_offset += bytes; > > > > > + } > > > > > + > > > > > + ret = rbd_flush(image); > > > > > + if (ret < 0) { > > > > > + error_setg_errno(errp, -ret, "Failed to flush the file"); > > > > > + goto out; > > > > > + } > > > > > + > > > > > + break; > > > > > + } > > > > > + case PREALLOC_MODE_OFF: > > > > > + ret = rbd_resize(image, offset); > > > > > > > > I'm not familiar enough w/ the QEMU block code, but why would the > > > > PREALLOC_MODE_FULL case not need to resize the image? > > > > > > PREALLOC_MODE_FULL need too, I did it just before the g_malloc0() in > > > this patch :-) > > > > Sorry I missed it. Would it make more sense to just do it before the > > switch statement so that you don't duplicate the code and resulting > > error handling? I guess just validate that the prealloc mode is > > supported before issuing the resize. > > > > Sure, it's more robust in this way. > > Thanks, > Stefano -- Jason