[all-commits] [llvm/llvm-project] 98e0b2: [Support] Revert posix_fallocate in resize_file
Fangrui Song via All-commits
all-commits at lists.llvm.org
Mon Dec 20 11:16:16 PST 2021
Author: Fangrui Song <i at maskray.me>
Date: 2021-12-20 (Mon, 20 Dec 2021)
[Support] Revert posix_fallocate in resize_file
This reverts 3816c53f040cc6aa06425978dd504b0bd5b7899c and removes follow-up
The original intention was to show error earlier (posix_fallocate time) than
later for ld.lld but it appears to cause some problems which make it not free.
* FreeBSD ZFS: EINVAL, not too bad.
* FreeBSD UFS: according to khng "devastatingly slow on freebsd because UFS on freebsd does not have preallocation support like illumos. It zero-fills."
* NetBSD: maybe EOPNOTSUPP
* Linux tmpfs: unless tmpfs is set up to use huge pages (requires CONFIG_TRANSPARENT_HUGE_PAGECACHE=y), I can consistently demonstrate ~300ms delay for a 1.4GiB output.
* Linux ext4: I don't measure any benefit, either backed by a hard disk or by a file in tmpfs.
* The current code organization of `defined(HAVE_POSIX_FALLOCATE)` costs us a macro dispatch for AIX.
I think we should just remove it. I think if posix_fallocate ever finds demonstrable benefit,
it is likely Linux specific and will not need HAVE_POSIX_FALLOCATE, and possibly opt-in by some specific programs.
In a filesystem with CoW and compression, the ENOSPC benefit may be lost as well.
Reviewed By: khng300
Differential Revision: https://reviews.llvm.org/D115957
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