On Nov 15 2016, Maxim Patlasov <mpatlasov@xxxxxxxxxxxxx> wrote:
On 11/15/2016 08:18 AM, Nikolaus Rath wrote:Ah, that makes sense. Are these two cases meant as examples, or is that
Could someone explain to me the meaning of the max_background andfuse uses max_background for cases where the total number of
congestion_threshold settings of the fuse module?
At first I assumed that max_background specifies the maximum number of
pending requests (i.e., requests that have been send to userspace but
for which no reply was received yet). But looking at fs/fuse/dev.c, it
looks as if not every request is included in this number.
simultaneous requests of given type is not limited by some other
natural means. AFAIU, these cases are: 1) async processing of direct
IO; 2) read-ahead. As an example of "natural" limitation: when
userspace process blocks on a sync direct IO read/write, the number of
requests fuse consumed is limited by the number of such processes
(actually their threads). In contrast, if userspace requests 1GB
direct IO read/write, it would be unreasonable to issue 1GB/128K==8192
fuse requests simultaneously. That's where max_background steps in.
an exhaustive list? Because I would have thought that other cases should
be writing of cached data (when writeback caching is enabled), and
asynchronous I/O from userspace...?
Also, I am not sure what you mean with async processing of direct
I/O. Shouldn't direct I/O always go directly to the file-system? If so,
how can it be processed asynchronously?