HAYASAKA Mitsuo <mitsuo.hayasaka.hu@xxxxxxxxxxx> writes: > Hi Yuan and Han-Wen, > > Thank you for your comments. > > (2012/07/06 22:58), Han-Wen Nienhuys wrote: >> On Fri, Jul 6, 2012 at 2:53 AM, Liu Yuan<namei.unix@xxxxxxxxx> wrote: >>> On 07/05/2012 06:50 PM, Mitsuo Hayasaka wrote: >>>> One of the ways to solve this is to make them tunable. >>>> In this series, the new sysfs parameter max_pages_per_req is introduced. >>>> It limits the maximum read/write size in fuse request and it can be >>>> changed from 32 to 256 pages in current implementations. When the >>>> max_read/max_write mount option is specified, FUSE request size is set >>>> per mount. (The size is rounded-up to page size and limited up to >>>> max_pages_per_req.) >>> >>> Why maxim 256 pages? If we are here, we can go further: most of object >>> storage system has object size of multiple to dozens of megabytes. So I >>> think probably 1M is too small. Our distribution storage system has 4M >>> per object, so I think at least maxim size could be bigger than 4M. >> >> The maximum pipe size on my system is 1M, so if you go beyond that, >> splicing from the FD won't work. >> >> Also, the userspace client must reserve a buffer this size so it can >> receive a write, which is a waste since most requests are much >> smaller. >> > > I checked the maximum pipe size can be changed using fcntl(2) or > /proc/sys/fs/pipe-max-size. It is clear that it is not a fixed value. > > Also, it seems that there is a request for setting the maximum number > of pages per fuse request to 4M (1024 pages). One of the reasons to > introduce the sysfs max_pages_per_req parameter is to set a threshold > of the maximum number of pages dynamically according to the > administrator's demand, and root can only change it. > > So, when the maximum value is required to be set to not more than the > pipe-max-size, the max_pages_per_req should be changed considering it. > It seems that the upper limit of this parameter does not have to be > not more than it. > > I'm planning to limit max_pages_per_req up to 1024 pages and add the > document to /Documentation/filesystems/fuse.txt, as follows. > > "the sysfs max_pages_per_req parameter can be changed from 32 to 1024. > The default is 32 pages. Generally, the pipe-max-size is 1M (256 pages) > and it is better to set it to not more than the pipe-max-size." Can't we just use pipe-max-size for the limit? Then we'll use the minimum of pipe-max-size and max_read/max_write for sizing the requests. Another comment: do we really need to allocate each and every request with space for the pages? I don't think that makes sense. Let's leave some small number of pages inline in the request and allocate a separate array if the number of pages is too large. There may even be some utilities in the kernel to handle dynamically sized page arrays (I haven't looked but I suspect there is). Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
