Index of /archives/linux/kernel.org/kernel/people/rml/O_STREAMING

 Name                                          Last modified      Size  Description
 Parent Directory                                                   -   
 IN_LIEU                                       2004-10-27 12:47   77   
 README                                        2002-10-08 11:42  1.2K  
 sha256sums.asc                                2023-04-26 06:12  1.0K  
 v2.4/                                         2013-01-26 00:42    -   

Attached patch implements an O_STREAMING file I/O flag which enables
manual drop-behind of pages.

If the file has O_STREAMING set then the user has explicitly said "this
is streaming data, I know I will not revisit this, do not cache
anything".  So we drop pages from the pagecache before our current
index.  We have to fiddle a bit to get writes working since we do
write-behind but the logic is there and it works.

Some numbers.  A simple streaming read to verify the pagecache effects:

        Streaming 1GB Read (avg of many runs, mem=2GB):
        O_STREAMING     Wall time       Change in Page Cache
        Yes             25.58s          0
        No              25.55s          +835MB

Another read with much more VM pressure:

        Streaming 1GB Read (avg of many runs, mem=8M)
        O_STREAMING     Wall time       Change in Page Cache
        Yes             25.76s          0
        No              29.01s          +1MB

And now the kicker:

        Kernel compile (make -j2) and concurrent streaming I/O
        (avg of two runs, mem=128M):
        O_STREAMING     Time to complete Kernel Compile
        Yes             3m27.863s
        No              4m15.818s

This is c/o Andrew Morton.