I've got two questions about mballoc's stream allocation.
First of all, in ext4_mb_regular_allocator(), I'm 99% sure this is a
bug:
/* if stream allocation is enabled, use global goal */
size = ac->ac_o_ex.fe_logical + ac->ac_o_ex.fe_len;
isize = i_size_read(ac->ac_inode) >> bsbits;
if (size < isize)
size = isize;
if (size < sbi->s_mb_stream_request &&
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(ac->ac_flags & EXT4_MB_HINT_DATA)) {
/* TBD: may be hot point */
spin_lock(&sbi->s_md_lock);
ac->ac_g_ex.fe_group = sbi->s_mb_last_group;
ac->ac_g_ex.fe_start = sbi->s_mb_last_start;
spin_unlock(&sbi->s_md_lock);
}
Shouldn't that be ">=", not "<". We want to use the values saved in
sbi->s_mb_last_{group,start} only if we are doing a stream allocation,
which would be true only if the file is *larger* than
s_mb_stream_request, no?
The second question I have is with regards to ext4_mb_use_best_found(),
we set sbi->s_mb_last_{group,start} on any data allocation; shouldn't we
only be setting those values only if we were doing a stream allocation
in the first place?
Otherwise, any kind of allocation will end up moving the global goal
block for stream allocations; even if it is a small allocation in the
middle of some block group caused by the flag EXT4_MB_HINT_NO_PREALLOC
being set.
Am I missing anything?
- Ted
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