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Date: Thu, 14 Aug 2008 14:49:32 -0700 From: Mingming Cao <cmm@...ibm.com> To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> Cc: Theodore Tso <tytso@....edu>, linux-ext4@...r.kernel.org Subject: Re: Bug in delayed allocation: really bad block layouts! 在 2008-08-13三的 16:22 +0530，Aneesh Kumar K.V写道： > On Tue, Aug 12, 2008 at 10:32:05PM -0400, Theodore Tso wrote: > > On Mon, Aug 11, 2008 at 11:45:24PM +0530, Aneesh Kumar K.V wrote: > > > On Mon, Aug 11, 2008 at 08:09:12PM +0530, Aneesh Kumar K.V wrote: > > > > Can you try this patch ? The patch make group preallocation use the goal > > > > block. > > > > > > > > > > Results with and without patch. > > > > > > http://www.radian.org/~kvaneesh/ext4/lg-fragmentation/ > > > > > > > My results match yours; seems to be a bit better, but it's not fixing > > the fundamental problem. With the patch: > > > > 26524: expecting 638190 actual extent phys 631960 log 1 len 1 > > 26527: expecting 638191 actual extent phys 631963 log 1 len 1 > > 26533: expecting 638192 actual extent phys 631976 log 1 len 5 > > 26534: expecting 638193 actual extent phys 631981 log 1 len 2 > > 26536: expecting 638194 actual extent phys 631984 log 1 len 6 > > 26538: expecting 638195 actual extent phys 631991 log 1 len 5 > > 26540: expecting 638196 actual extent phys 631997 log 1 len 2 > > 26545: expecting 638197 actual extent phys 632009 log 1 len 1 > > 26546: expecting 638198 actual extent phys 632010 log 1 len 6 > > 26604: expecting 638199 actual extent phys 632156 log 1 len 1 > > > > Useing debugfs's stat command to look at the blocks: > > > > 26524: (0):638189, (1):631960 > > 26527: (0):638190, (1):631963 > > 26533: (0):638191, (1-5):631976-631980 > > 26534: (0):638192, (1-2):631981-631982 > > 26536: (0):638193, (1-6):631984-631989 > > 26538: (0):638194, (1-5):631991-631995 > > 26540: (0):638195, (1-2):631997-631998 > > 26545: (0):638196, (1):632009 > > 26546: (0):638197, (1-6):632010-632015 > > I am not sure why we are getting single block request for inodes > 26524 etc. With delayed alloc we should have got 2 block request. > > > > > Out of curiosity, I also probed the inode numbers that were out of > > sequence from above. They seem to be mostly allocating out of the > > numbers used for the second extent, above. > > > > 26526: (0):631961 > > 26526: (0):631962 > > 26528: (0):631964 > > 26529: (0):411742 > > 26530: (0):631965 > > 26531: (0-1):631966-631967 > > 26532: (0-7):631968-631975 > > 26535: (0):631983 > > 26537: (0):631990 > > 26541: (0-7):631999-632006 > > 26542: (0):632007 > > 26543: (0):632008 > > 26544: (0):411743 > > 26547: (0):632016 > > > > Inode Pathname > > 26524 /lib/rhythmbox/plugins/lyrics/LyricsConfigureDialog.py > > 26525 /lib/rhythmbox/plugins/lyrics/LyrcParser.py > > 26526 /lib/rhythmbox/plugins/lyrics/LyricsParse.py > > 26527 /lib/rhythmbox/plugins/lyrics/LyricsConfigureDialog.pyc > > 26528 /lib/rhythmbox/plugins/lyrics/WinampcnParser.py > > 26529 /lib/rhythmbox/plugins/magnatune > > 26530 /lib/rhythmbox/plugins/magnatune/magnatune_logo_color_small.png > > 26531 /lib/rhythmbox/plugins/magnatune/magnatune.rb-plugin > > 26532 /lib/rhythmbox/plugins/magnatune/magnatune-prefs.glade > > 26533 /lib/rhythmbox/plugins/magnatune/MagnatuneSource.pyc > > 26534 /lib/rhythmbox/plugins/magnatune/__init__.py > > 26535 /lib/rhythmbox/plugins/magnatune/BuyAlbumHandler.py > > 26536 /lib/rhythmbox/plugins/magnatune/magnatune-purchase.glade > > 26537 /lib/rhythmbox/plugins/magnatune/TrackListHandler.py > > 26538 /lib/rhythmbox/plugins/magnatune/MagnatuneSource.py > > 26539 /lib/rhythmbox/plugins/magnatune/magnatune_logo_color_tiny.png > > 26540 /lib/rhythmbox/plugins/magnatune/__init__.pyc > > 26541 /lib/rhythmbox/plugins/magnatune/magnatune-loading.glade > > 26542 /lib/rhythmbox/plugins/magnatune/TrackListHandler.pyc > > 26543 /lib/rhythmbox/plugins/magnatune/BuyAlbumHandler.pyc > > 26544 /lib/rhythmbox/plugins/audioscrobbler > > 26546 /lib/rhythmbox/plugins/audioscrobbler/audioscrobbler-prefs.glade > > 26547 /lib/rhythmbox/plugins/audioscrobbler/audioscrobbler-ui.xml > > > > Looks like we still have some problems with the block allocator... > > The problem is with delalloc and mballoc locality group. With delalloc > we use pdflush to write the pages. Small file allocation use a per-cpu > prealloc space. In my understanding using Per-CPU prealloc space is > fine without delalloc. Because without delalloc get_block happens in the > process context at write_begin and OS scheduler will not schedule the > task to other CPU unless needed. > > With delalloc we have pdflush doing block allocation and using per-cpu > may not really help here. I wonder if it still make sense for using per~cpu group locality allocation with delalloc, with the fact that all block allocation is done via pdflush? > So i tried a small patch as below. But that > didn't help much. Also the patch would increase contention on the > locality group mutex. So i guess the change is not worth. > > But with delalloc we should have got multiple block request together. > That implies we should get a single get_block request for the whole > file. I will have to instrument the kernel to understand why it is not > happening. > I am courious to know this too. Why we get single block allocation request for delalloc? Mingming -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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