ru.unix.bsd

 
 - RU.UNIX.BSD ------------------------------------------------------------------
 From : Slawa Olhovchenkov                   2:5030/500     22 Sep 2007  16:42:06
 To : All
 Subject : Вести с полей
 -------------------------------------------------------------------------------- 
 

 
 bde         2007-07-10 13:20:24 UTC
 
   FreeBSD src repository
 
   Modified files:
     sys/fs/msdosfs       msdosfs_fat.c msdosfsmount.h
   Log:
   Don't use almost perfectly pessimal cluster allocation.  Allocation
   of the the first cluster in a file (and, if the allocation cannot be
   continued contiguously, for subsequent clusters in a file) was randomized
   in an attempt to leave space for contiguous allocation of subsequent
   clusters in each file when there are multiple writers.  This reduced
   internal fragmentation by a few percent, but it increased external
   fragmentation by up to a few thousand percent.
 
   Use simple sequential allocation instead.  Actually maintain the fsinfo
   sequence index for this.  The read and write of this index from/to
   disk still have many non-critical bugs, but we now write an index that
   has something to do with our allocations instead of being modified
   garbage.  If there is no fsinfo on the disk, then we maintain the index
   internally and don't go near the bugs for writing it.
 
   Allocating the first free cluster gives a layout that is almost as good
   (better in some cases), but takes too much CPU if the FAT is large and
   the first free cluster is not near the beginning.
 
   The effect of this change for untar and tar of a slightly reduced copy
   of /usr/src on a new file system was:
 
   Before (msdosfs 4K-clusters):
   untar:  459.57 real              untar from cached file (actually a pipe)
   tar:    342.50 real              tar from uncached tree to /dev/zero
   Before (ffs2 soft updates 4K-blocks 4K-frags)
   untar:   39.18 real
   tar:     29.94 real
   Before (ffs2 soft updates 16K-blocks 2K-frags)
   untar:   31.35 real
   tar:     18.30 real
 
   After (msdosfs 4K-clusters):
   untar    54.83 real
   tar      16.18 real
 
   All of these times can be improved further.
 
   With multiple concurrent writers or readers (especially readers), the
   improvement is smaller, but I couldn't find any case where it is
   negative.  342 seconds for tarring up about 342 MB on a ~47MB/S partition
   is just hard to unimprove on.  (This operation would take about 7.3
   seconds with reasonably localized allocation and perfect read-ahead.)
   However, for active file systems, 342 seconds is closer to normal than
   the 16+ seconds above or the 11 seconds with other changes (best I've
   measured -- won easily by msdosfs!).  E.g., my active /usr/src on ffs1
   is quite old and fragmented, so reading to prepare for the above
   benchmark takes about 6 times longer than reading back the fresh copies
   of it.
 
   Approved by:    re (kensmith)
 
   Revision  Changes    Path
   1.40      +4 -5      src/sys/fs/msdosfs/msdosfs_fat.c
   1.38      +1 -1      src/sys/fs/msdosfs/msdosfsmount.h
 ... Винда не пpиходит одна. (c) Microsoft Team
 --- GoldED+/BSD 1.1.5
  * Origin:  (2:5030/500)
 
 

Вернуться к списку тем, сортированных по: возрастание даты  уменьшение даты  тема  автор