Revert "Graphite Compilation"

This reverts commit eab6e9753740da9a91555ab963c746fc9b7f479a.
Revert "genalloc: stop crashing the system when destroying a pool"

This reverts commit 899ef84c04297aeef1c94cf02b63738713f76605.
block: Reserve only one queue tag for sync IO if only 3 tags are available

In case a device has three tags available we still reserve two of them
for sync IO. That leaves only a single tag for async IO such as
writeback from flusher thread which results in poor performance.

Allow async IO to consume two tags in case queue has three tag availabe
to get a decent async write performance.

This patch improves streaming write performance on a machine with such disk
from ~21 MB/s to ~52 MB/s. Also postmark throughput in presence of
streaming writer improves from 8 to 12 transactions per second so sync
IO doesn't seem to be harmed in presence of heavy async writer.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: klozz <xxx.reptar.rawrr.xxx@gmail.com>
mm: Added filesystem dynamic read-ahead (Credits to Chad Gooldman)

Signed-off-by: klozz <xxx.reptar.rawrr.xxx@gmail.com>