[mythtv-commits] Ticket #9458: [patch] posix_fadvice usage

MythTV noreply at mythtv.org
Fri Jan 7 18:39:00 UTC 2011


#9458: [patch] posix_fadvice usage
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 Reporter:  jiri.fojtasek@…             |          Owner:  danielk
     Type:  Patch - Bug Fix             |         Status:  assigned
 Priority:  minor                       |      Milestone:  0.25
Component:  MythTV - General            |        Version:  Trunk Head
 Severity:  medium                      |     Resolution:
 Keywords:                              |  Ticket locked:  0
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Changes (by danielk):

 * owner:   => danielk
 * status:  new => assigned


Comment:

 Jiri, I noticed that one of the fixes was signed by a "--setra". Is there
 a thread somewhere with longer explanations of each of the changes? The
 main thing I see here is that these advise calls appear to be interpreted
 globally rather than per file descriptor. i.e. if process A is reading
 file X on fd 2 at location 1024 and process B is writing to X fd 3 then
 when B issues a POSIX_FADV_WONTNEED for the data before location 2048,
 process A now needs to read from the disk rather than reading from the
 cache. This would be caused by the OS is not being smart enough to realize
 that even if process B doesn't plan to read the file soon, process A is
 reading the file with the SEQUENTIAL attribute and will soon read bytes
 1025 through 2048.

-- 
Ticket URL: <http://code.mythtv.org/trac/ticket/9458#comment:1>
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