Let's take your demonology warlock with 0/5 demonic embrace, raidbuffed (+50 from divine spirit +20 blackened basilisk, 18 from motw, +10% from human bonus, +10% from bok)
160 (this is your average, naked base spirit at 70 as ctprofiles claims to) + 50 +18 +20 =248
248*1.2=297
Round up to 300, take another 80 from gear (even if 50 spirit from a spelldmg/hit/crit gear might be more then you may ever dream off), round up again to 400 spirit.
Now let's use
[Bangle of Endless Blessings] +
[Darkmoon Card: Blue Dragon], reaching 12% chance for meditation. You a a smart warlock doing 25 casts per minute, ending in 3 meditation states at perfect interval of 45s (generously 23 ticks)
400/5+15*0.15*23*=327 mana/minute
Wow, thats awsome! Losing 2 trinketslots for this huge amount of mana per minute :/
So, as you may see, this is no real option. What can you do?
a) get a personal healer
b) get a shadowpriest for your group
c) sacrifice your felhunter or your voidwalker (check your hp:mp ratio and deside)
d) use more consumeables to restore mana
e) you allready reached the maximum possible, congratulation!
f) be smart, use bandages
g) drop lology and learn affliction for darkpact :/