RFR: 8333783: java/nio/channels/FileChannel/directio/DirectIOTest.java is unstable with AV software [v2]

[Aleksey Shipilev]

> This test routinely fails on our instances that have AV software enabled: that software apparently reads the file in background on access, which trips the very sensitive "is file in cache" test. It looks like there is a reliable way to mitigate this by keeping the file open, and attempting the (read|write)+check several times, with cache flush in between.
> 
> This is not perfect, but works in practice. Second attempt seems to work in >99% of the cases, we are doing 3 attempts to make test extra reliable.
> 
> Additional testing:
>  - [x] Linux AArch64 server fastdebug; sensitivity check: dropped `DIRECT` from the test, test starts failing immediately
>  - [x] Linux AArch64 server fastdebug, test does not fail after 100x repetitions
>  - [x] Linux AArch64 server fastdebug, test does not fail after 10000x repetitions

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Remove unnecessary changes

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/26961/files
  - new: https://git.openjdk.org/jdk/pull/26961/files/763760fa..ccacf797

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26961&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26961&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/26961.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26961/head:pull/26961

PR: https://git.openjdk.org/jdk/pull/26961