On Wed, Jan 28, 2015 at 11:27:13AM -0800, Nikhilesh Reddy wrote: > Hi > I am working on a 64 bit Android device and have been trying to > improve performance for stream based data download (for example an > ftp) > The device has 3GB of ram and the dirty_ratio and > dirty_background_ratio are set to 5 and 1 respectively. > > Kernel 3.10 , Highmem is not enabled and the backing device is a > emmc and checksumming is not enabled Ok, 3.10 kernel is new enough that stable page writes only apply to devices that demand it, and apparently your eMMC demands it. > I noticed when profiling writes that if we dont use streamed IO (ie. > use write of whatever size data was read on the tcp stream) there > are some writes that seem to get blocked on > wait_for_stable_page. > > If I force the writes to be buffered in the userspace and ensure > writing 4k chunks the writes never seem to stall. That's consistent with a page being partially dirtied, written out, and partially dirtied again before write-out finishes. If you buffer the incoming data such that a page is only dirtied once, you'll never notice wait_for_stable_page. Are you explicitly forcing writeout (i.e. fsync()) after every chunk arrives? Or, is the rate of incoming data high enough such that we hit either dirty*ratio limit? It isn't too hard to hit 30MB these days. Why are you lowering the ratios from their defaults? > I noticed there was earlier discussion on this and idea were > proposed to use snapshotting of the pages to avoid stalls... > For example: https://lwn.net/Articles/546658/ > > But this seems to only snapshot ext3 ... (unless i misunderstood > what the patch is doing) > > Is there a similar patch to snapshot the buffers to not stall the > writes for ext4? No, there is not -- the problem with the snapshot solution is that it requires page allocations when the FS is (potentially) trying to reclaim memory by writing out dirty pages. --D > Please let me know. > > I would really appreciate any help you can give me. > > > -- > Thanks > Nikhilesh Reddy > > Qualcomm Innovation Center, Inc. > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > a Linux Foundation Collaborative Project. > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
