search for: readahead

Hi, I am trying to educate myself on prefetching/readahead algorithm for Lustre''s read. For a starter I only have two simple questions. 1 - Does Lustre detect linear or random I/O pattern or it always triggers readahead? 2 - If readahead is triggered, how many pages are read in addition to what is necessary? Thanks, Arifa.

Simpler, and including tests. Rich.

Hi, We have file readahead to do asyn file read, but has no metadata readahead. For a list of files, their metadata is stored in fragmented disk space and metadata read is a sync operation, which impacts the efficiency of readahead much. The patches try to add meatadata readahead for btrfs. In btrfs, metadata is stored in...

A suggested readahead filter. I've only lightly tested this, but it seems to work fine with qemu-img convert. The commit needs proper tests. Rich.

...-utils (kernel-utils-2.4-13.1.80). I'm sure these are all propagated from upstream, but I hope someone could have a quick look to verify this and see if we either can push complaints upwards, or provide local fixes. The kernel-utils package provides several 'kernel-type' functions - readahead and readahead_early and also the cpuspeed have a few problems; readahead 'reads ahead' (stats to copy to cache for speedy access?) the files found in /etc/readahead.files. While most of these files are various images and common binaries, some are libraries which have been replaced by ne...

...ugh snippets of code as to be easier to read when left as-is; but when the scope is indeed function-wide or across multiple exit paths, it is nicer to use the macro for automatic unlock. Signed-off-by: Eric Blake <eblake@redhat.com> --- filters/log/log.c | 10 ++++------ filters/readahead/readahead.c | 15 +++++---------- filters/log/Makefile.am | 5 ++++- filters/readahead/Makefile.am | 5 ++++- 4 files changed, 17 insertions(+), 18 deletions(-) diff --git a/filters/log/log.c b/filters/log/log.c index 02a2522..513d390 100644 --- a/filters/log/log.c +++ b/filters/log/log.c...

The readahead filter is a self-configuring filter that makes sequential reads faster when the plugin is slow (and all of the plugins we use here are always slow). I observed the behaviour of the readahead filter with our qcow2 overlay when converting a guest from a vCenter source. Even when doing random reads,...

Sysctl Values ------------------------------------------- net.core.rmem_max = 16777216 net.core.wmem_max = 16777216 net.ipv4.tcp_rmem = 4096 87380 16777216 net.ipv4.tcp_wmem = 4096 65536 16777216 net.ipv4.tcp_window_scaling = 1 # vm.max-readahead = ? # vm.min-readahead = ? # HW Controler Off # max-readahead = 1024 # min-readahead = 256 # Memory over-commit # vm.overcommit_memory=2 # Memory to activate bdflush # vm.bdflush="40 500 0 0 500 3000 60 20 0" -------------------------------------------- What's the deal with the op...

...ere VMware VCenter server's Tomcat HTTPS server stops responding to > requests (or rather, responds only with 503 errors). The server later > recovers and in fact because of the retry filter the conversion > usually succeeds, but I found that we can avoid the problem by > disabling readahead. > --- > v2v/nbdkit_sources.ml | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > Is it just a matter of readahead requesting too much data at once? Is it time to start revisiting the idea of moving the core of the 'blocksize' filter into the server itself...

...still testing this fix, so let's hold off the review for the moment. Also it may be better to specifically identify problematic servers rather than disabling this for every curl source. eg. I suspect that the problem is the Java server used by VCenter, so we might think about only disabling readahead for that single case. Rich.

...simplest solution to this problem. There are two other possible fixes I considered: Increase the documented limit (see http://libguestfs.org/virt-v2v-input-vmware.1.html#vddk:-esxi-nfc-service-memory-limits). However at the moment we know the current limit works through extensive testing (without readahead), plus I have no idea nor any way to test if larger limits are supported by all versions of VMware new and old. The limit we are recommending at the moment is the one documented by VMware. Also this would require users to change their VMware settings again, and no doubt introduce confusion for pe...

I'm trying to replicate the features of the qemu curl plugin in nbdkit's curl plugin, in order that we can use nbdkit in virt-v2v to access VMware servers. I've implemented everything else so far [not posted yet] except for readahead. To my surprise actually, qemu's curl driver implements readahead itself. I thought it was a curl feature. I'm not completely clear _how_ it works in qemu, but it seems like it's maintaining an array of outstanding AIO requests, searching those first to see if one contains the read d...

...4 type protocol/client option transport-type ib-verbs option remote-host gluster4 option remote-subvolume iothreads end-volume volume client-stripe-5 type protocol/client option transport-type ib-verbs option remote-host gluster5 option remote-subvolume iothreads end-volume volume readahead-gluster1 type performance/read-ahead option page-count 4 # 2 is default option force-atime-update off # default is off subvolumes client-stripe-1 end-volume volume readahead-gluster2 type performance/read-ahead option page-count 4 # 2 is default option force-atime...

...ke this: nbdkit: vddk[3]: error: [NFC ERROR] NfcFssrvrProcessErrorMsg: received NFC error 5 from server: Failed to allocate the requested 33554456 bytes We already increase the maximum request size by changing the configuration on the VMware server, but it's not sufficient for VDDK with the readahead filter. As readahead is only an optimization, the simplest solution is to disable this filter when we're using nbdkit-vddk-plugin. Thanks: Ming Xie --- v2v/nbdkit_sources.ml | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/v2v/nbdkit_sources.ml b/v2v/nbdkit_sources...

On Fri, Sep 20, 2019 at 10:28:18AM +0100, Richard W.M. Jones wrote: >The readahead filter is a self-configuring filter that makes >sequential reads faster when the plugin is slow (and all of the >plugins we use here are always slow). > >I observed the behaviour of the readahead filter with our qcow2 >overlay when converting a guest from a vCenter source. Even when...

Quick question... The docs for vfs readahead mention Windows Vista, but what about modern Windows versions? Windows Server 2016 or Windows Server 2019? Thank you, -- BOB BUCK SENIOR PLATFORM SOFTWARE ENGINEER SKIDMORE, OWINGS & MERRILL 7 WORLD TRADE CENTER 250 GREENWICH STREET NEW YORK, NY 10007 T (212) 298-9624 ROBERT.BUCK at SOM.C...

...4 type protocol/client option transport-type ib-verbs option remote-host gluster4 option remote-subvolume iothreads end-volume volume client-stripe-5 type protocol/client option transport-type ib-verbs option remote-host gluster5 option remote-subvolume iothreads end-volume volume readahead-gluster1 type performance/read-ahead option page-count 4 # 2 is default option force-atime-update off # default is off subvolumes client-stripe-1 end-volume volume readahead-gluster2 type performance/read-ahead option page-count 4 # 2 is default option force-atime...

...e conversion step where VMware VCenter server's Tomcat HTTPS server stops responding to requests (or rather, responds only with 503 errors). The server later recovers and in fact because of the retry filter the conversion usually succeeds, but I found that we can avoid the problem by disabling readahead. --- v2v/nbdkit_sources.ml | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/v2v/nbdkit_sources.ml b/v2v/nbdkit_sources.ml index f5e919116..7c177e358 100644 --- a/v2v/nbdkit_sources.ml +++ b/v2v/nbdkit_sources.ml @@ -99,12 +99,12 @@ let common_create ?bandwidth ?extra_deb...

This adds a binding for 'blockdev --setra', allowing you to adjust the readahead parameter for filesystems and devices. --- daemon/blockdev.c | 30 ++++++++++++++++++++---------- generator/actions.ml | 14 ++++++++++++++ 2 files changed, 34 insertions(+), 10 deletions(-) diff --git a/daemon/blockdev.c b/daemon/blockdev.c index 8a7b1a8..6e8821d 100644 --- a/daemon/blockdev....

...seeing a problem where it appears that windows is not reading data far enough ahead (or maybe at all) to keep the pipeline full. From assessing the load on samba, it is a apparent that much of its time is spent idle. The characteristics of the load suggest that WinXP or Win2000 is not requesting readahead far enough to be useful. My link roundtrip latency is around .4 ms beyond the data transmission time, the samba servicing time for 32K of data (32K is the blocksize I'm using) is about .27 ms, and the wire time for 32K of data should be around .27ms on GigE. I understand that it is necessary...