glusterfs.git/xlators/features/bit-rot/src/bitd/bit-rot-scrub.h, branch v3.7.4

features/bitrot: handle scrub states via state machine

2015-07-09T10:29:01+00:00

    Backport of http://review.gluster.org/11149

A bunch of command line options for scrubber tempted the use of
state machine to track current state of scrubber under various
circumstances where the options could be in effect.

Change-Id: Id614bb2e6af30a90d2391ea31ae0a3edeb4e0d69
BUG: 1226666
Signed-off-by: Venky Shankar 
Reviewed-on: http://review.gluster.org/11541
Reviewed-by: Raghavendra Bhat 
Tested-by: Gluster Build System

features/bitrot: reimplement scrubbing frequency

2015-05-31T04:14:10+00:00

This patch reimplments existing scrub-frequency mechanism used
to schedule scrubber runs. Existing mechanism uses periodic
sleeps (waking up periodically on minimum granularity) and
performing a number of tracking checks based on counters and
sleep times. This patch does away with all the nifty counters
and uses timer-wheel to schedule scrub runs.

Scheduling changes are peformed by merely calculating the new
expiry time and calling mod_timer() [mod_timer_pending() in
some cases] making the code more debuggable and easier to
follow. This also introduces "hourly" scrubbing tunable as an
aid for testing scrubbing during development/testing cycle.

One could also implement on-demand scrubbing with ease: by
invoking mod_timer() with an expiry of one (1) second, thereby
scheduling a scrub run the very next second.

Change-Id: I6c7c5f0c6c9f886bf574d88c04cde14b76e60a8b
BUG: 1224647
Signed-off-by: Venky Shankar 
Reviewed-on: http://review.gluster.org/10902
Tested-by: Gluster Build System 
Tested-by: NetBSD Build System

features/bitrot: Throttle filesystem scrubber

2015-05-10T12:29:31+00:00

This patch introduces multithreaded filesystem scrubber based
on throttling option configured for a particular volume. The
implementation "logically" breaks scanning and scrubbing with
the number of scrubber threads auto-configured depending upon
the throttle configuration. Scanning (crawling) is left single
threaded (per brick) with entries scrubbed in bulk. On reaching
this "bulk" watermark, scanner waits until entries are scrubbed.
Bricks for a particular volume have a set of thread(s) assigned
for scrubbing, with entries for each brick scrubbed in a round
robin fashion to avoid scrub "stalls" when a brick (out of N
bricks) is under active scrubbing.

This mechanism helps us implement "pause/resume" with ease: all
one need to do is to cleanup scrubber threads and let the main
scanner thread "wait" untill scrubbing is resumed (where the
scrubber thread(s) are spawned again), therefore continuing
where we left off (unless we restart the deamons, where crawl
initiates from root directory again, but I guess that's OK).

[
    NOTE:

    Throttling is optional for the signer daemon, without which
    it runs full throttle. However, passing "-DBR_RATE_LIMIT_SIGNER"
    predefined in CFLAGS enables CPU throttling (during checksum
    calculation) thereby avoiding high CPU usage.
]

Subsequent patches would introduce CPU throttling during hash
calculation for scrubber.

> Change-Id: I5701dd6cd4dff27ca3144ac5e3798a2216b39d4f
> BUG: 1207020
> Signed-off-by: Venky Shankar 
> Reviewed-on: http://review.gluster.org/10511
> Tested-by: Gluster Build System 
> Reviewed-by: Vijay Bellur 

Change-Id: I5a125b2d0ac7dafd3e278b7fe4c6c9dd07af76dd
Signed-off-by: Venky Shankar 
BUG: 1220041
Reviewed-on: http://review.gluster.org/10720
Tested-by: Gluster Build System 
Reviewed-by: Gaurav Kumar Garg

features/bit-rot: filesystem scrubber

2015-03-24T17:55:51+00:00

Scrubber performs signature verification for objects that were
signed by signer. This is done by recalculating the signature
(using the hash algorithm the object was signed with) and
verifying it aginst the objects persisted signature. Since the
object could be undergoing IO opretaion at the time of hash
calculation, the signature may not match objects persisted
signature. Bitrot stub provides additional information about
the stalesness of an objects signature (determinted by it's
versioning mechanism). This additional bit of information is
used by scrubber to determine the staleness of the signature,
and in such cases the object is skipped verification (although
signature staleness is performed twice: once before initiation
of hash calculation and another after it (an object could be
modified after staleness checks).

The implmentation is a part of the bitrot xlator (signer) which
acts as a signer or scrubber based on a translator option. As
of now the scrub process is ever running (but has some form of
weak throttling mechanism during filesystem scan). Going forward,
there needs to be some form of scrub scheduling and IO throttling
(during hash calculation) tunables (via CLI).

Change-Id: I665ce90208f6074b98c5a1dd841ce776627cc6f9
BUG: 1170075
Original-Author: Raghavendra Bhat 
Original-Author: Venky Shankar 
Signed-off-by: Venky Shankar 
Reviewed-on: http://review.gluster.org/9914
Tested-by: Vijay Bellur 
Reviewed-by: Vijay Bellur