ObjectCacher: remove max_bytes and max_ob arguments to trim()

These are never passed, so replace them with the defaults.

Backport: emperor, dumpling
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
(cherry picked from commit bf8cf2d6d21a204a099347f3dcd5b48100b8c445)
ObjectCacher: use uint64_t for target and max values

All the options are uint64_t, but the ObjectCacher was converting them
to int64_t. There's never any reason for these to be negative, so
change the type.

Adjust a few conditionals so that they only convert known-positive
signed values to uint64_t before comparing with the target and max
values. Leave the actual stats accounting as loff_t for now, since
bugs in accounting will have bad effects if negative values wrap
around.

Backport: emperor, dumpling
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
(cherry picked from commit db034acf546a72739ff6543241543f3bd651f3ae)
librbd: remove limit on number of objects in the cache

The number of objects is not a significant indicated of when data
should be written out for rbd. Use the highest possible value for
number of objects and just rely on the dirty data limits to trigger
flushing. When the number of objects is low, and many start being
flushed before they accumulate many requests, it hurts average request
size and performance for many concurrent sequential writes.

Fixes: #7385
Backport: emperor, dumpling
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
(cherry picked from commit 0559d31db29ea83bdb6cec72b830d16b44e3cd35)