Limit read size in File::read_to_end loop

[ChrisDenton]

Fixes #110650.

Windows file reads have perf overhead that's proportional to the buffer size. When we have a reasonable expectation that we know the file size, we can set a reasonable upper bound for the size of the buffer in one read call.

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[joshtriplett]

Please don't add this amount of additional space when reading (for instance) an 8 byte file. If we need a bit of slack to make sure we've gotten EOF, that's fine, but let's not add 1024 bytes or more to an 8 byte read.

[joshtriplett]

@bors r+ rollup=never

[bors]

📌 Commit f74fe8b has been approved by joshtriplett

It is now in the queue for this repository.

[bors]

⌛ Testing commit f74fe8b with merge 9de7d91...

[bors]

☀️ Test successful - checks-actions
Approved by: joshtriplett
Pushing 9de7d91 to master...

[rust-timer]

Finished benchmarking commit (9de7d91): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.6%	[-0.6%, -0.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.6%	[-0.6%, -0.6%]	1

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.7%	[-2.2%, -0.7%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.7%	[-2.2%, -0.7%]	3

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-0.6%	[-0.6%, -0.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.6%	[-0.6%, -0.6%]	1