Use bytes for maximum size of linear memory with pooling #8628

alexcrichton · 2024-05-15T17:57:56Z

This commit changes configuration of the pooling allocator to use a byte-based unit rather than a page based unit. The previous PoolingAllocatorConfig::memory_pages configuration option configures the maximum size that a linear memory may grow to at runtime. This is an important factor in calculation of stripes for MPK and is also a coarse-grained knob apart from StoreLimiter to limit memory consumption. This configuration option has been renamed to max_memory_size and documented that it's in terms of bytes rather than pages as before.

Additionally the documented constraint of max_memory_size must be smaller than static_memory_bound is now additionally enforced as a minor clean-up as part of this PR as well.

This commit changes configuration of the pooling allocator to use a byte-based unit rather than a page based unit. The previous `PoolingAllocatorConfig::memory_pages` configuration option configures the maximum size that a linear memory may grow to at runtime. This is an important factor in calculation of stripes for MPK and is also a coarse-grained knob apart from `StoreLimiter` to limit memory consumption. This configuration option has been renamed to `max_memory_size` and documented that it's in terms of bytes rather than pages as before. Additionally the documented constraint of `max_memory_size` must be smaller than `static_memory_bound` is now additionally enforced as a minor clean-up as part of this PR as well.

fitzgen

LGTM but I am confused about one thing and have Opinions and Concerns about writing the constant value directly all over the place

crates/cli-flags/src/lib.rs

fitzgen · 2024-05-15T18:17:02Z

crates/fuzzing/src/generators/config.rs

@@ -76,7 +76,7 @@ impl Config {
        if let InstanceAllocationStrategy::Pooling(pooling) = &mut self.wasmtime.strategy {
            // One single-page memory
            pooling.total_memories = config.max_memories as u32;
-            pooling.memory_pages = 10;
+            pooling.max_memory_size = 10 * 65535;


This should be 65536 right? If you instead want the max address it should be 10 * 65536 - 1.

Also lets use named constants for the Wasm page size so that it is easier to find uses and update in the future for the custom-page-sizes proposal. We have it defined in wasmtime_types already, FWIW, and this could use that here:

wasmtime/crates/types/src/lib.rs

Line 1493 in c477424

pub const WASM_PAGE_SIZE: u32 = 0x10000;

Ah yeah 65535 is a typo here, and everywhere else, but I'm hesitant to go through all the work to import a constant in all these places since it's all in tests anyway and all the values are basically random constants. In the future the wasm page size won't be constant as well so it feels weird to proliferate usage of the constant... I can change these to >>16 and <<16 though where appropriate perhaps to reduce the risk of typos.

fitzgen · 2024-05-15T18:17:45Z

crates/fuzzing/src/generators/config.rs

@@ -135,7 +135,7 @@ impl Config {
            if pooling.total_memories < 1
                || pooling.total_tables < 5
                || pooling.table_elements < 1_000
-                || pooling.memory_pages < 900
+                || pooling.max_memory_size < (900 * 65536)


ditto regarding named constant

fitzgen · 2024-05-15T18:19:16Z

crates/fuzzing/src/generators/config.rs

-                if pooling.memory_pages == 0 {
-                    pooling.memory_pages = 1;
+                if pooling.max_memory_size == 0 {
+                    pooling.max_memory_size = 65535;


Also confused about 65535 here since that isn't a multiple of the page size, so this will disallow any non-zero-length memories, assuming we don't do rounding elsewhere in this PR?

fitzgen · 2024-05-15T18:19:59Z

crates/fuzzing/src/generators/config.rs

+            cfg.max_memory32_pages = min / 65536;
+            cfg.max_memory64_pages = min / 65535;


Also confused about 65535 vs 65536 here.

And ditto about named constants on everything here.

crates/wasmtime/src/config.rs

fitzgen · 2024-05-15T18:22:50Z

crates/wasmtime/src/runtime/vm/instance/allocator/pooling.rs

@@ -703,7 +704,7 @@ mod test {
        let config = PoolingInstanceAllocatorConfig {
            limits: InstanceLimits {
                total_memories: 1,
-                memory_pages: 0x10001,
+                max_memory_size: (1 << 32) + 65536,


named constant, even tho it's just a test. we want to make sure we are actually testing sizes that wasm could potentially grow to, and not accidentally just testing rounding behavior or something.

Could you expand on this? I could see a comment going here but I'm not sure otherwise what you're looking for in terms of a constant?

If the goal is to test behavior with N wasm pages of capacity, then we should make sure we are actually doing that (as opposed to testing with unaligned capacity) and using a constant helps in this scenario. I feel like the typos are evidence that we can mess this up.

Additionally, having a constant that we can grep for all uses of will make it easier to support the custom-page-sizes proposal down the line: we have a list of uses that we can turn into method calls if necessary, and a list of tests that we might want to update or copy and tweak.

The meaning of this test has sort of been updated and lost a bit over time as I've been tweaking settings. This isn't specifically testing for unalignment or anything like that it's just one size being bigger than the other and various bits and pieces have been lost to translation over time.

I'm gonna go ahead and merge this as-is but we can of course update tests afterwards. I'm basically just somewhat doubtful if it's worth the effort to try to document all tests for precisely what they're doing page-wise and such. I don't think any of the tests really need to be updated with custom-page-sizes since they're all using wasm memories of 64k pages and the tests for custom-page-sizes are going to be pretty orthogonal anyway. Much of the time the page limits are just to reduce VM memory reservations anyway and don't have much to do with page sizes.

fitzgen · 2024-05-15T18:23:49Z

crates/wasmtime/src/runtime/vm/instance/allocator/pooling/memory_pool.rs

@@ -767,7 +763,7 @@ mod tests {
                    max_tables_per_module: 0,
                    max_memories_per_module: 3,
                    table_elements: 0,
-                    memory_pages: 1,
+                    max_memory_size: 65536,


fitzgen · 2024-05-15T18:24:31Z

tests/all/async_functions.rs

@@ -344,7 +344,9 @@ async fn fuel_eventually_finishes() {
 #[tokio::test]
 async fn async_with_pooling_stacks() {
    let mut pool = crate::small_pool_config();
-    pool.total_stacks(1).memory_pages(1).table_elements(0);
+    pool.total_stacks(1)
+        .max_memory_size(65536)


ditto in this file's changes

fitzgen · 2024-05-15T18:26:48Z

tests/all/limits.rs

@@ -354,7 +354,7 @@ fn test_pooling_allocator_initial_limits_exceeded() -> Result<()> {
    let mut pool = crate::small_pool_config();
    pool.total_memories(2)
        .max_memories_per_module(2)
-        .memory_pages(5)
+        .max_memory_size(5 * 65536)


okay I am going to stop saying "ditto about named constants" now and assume you will go over the diff yourself to catch all of them at this point

github-actions · 2024-05-15T18:45:09Z

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github-actions · 2024-05-15T18:45:28Z

Label Messager: wasmtime:config

It looks like you are changing Wasmtime's configuration options. Make sure to
complete this check list:

If you added a new Config method, you wrote extensive documentation for
it.

Our documentation should be of the following form:

Short, simple summary sentence.

More details. These details can be multiple paragraphs. There should be
information about not just the method, but its parameters and results as
well.

Is this method fallible? If so, when can it return an error?

Can this method panic? If so, when does it panic?

# Example

Optional example here.

If you added a new Config method, or modified an existing one, you
ensured that this configuration is exercised by the fuzz targets.

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Often, all that is required of you is to ensure that there is a knob for this
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alexcrichton · 2024-05-16T15:29:50Z

I've updated with <<16 and >>16 to reduce the risk of typos, but I'm curious what you think of my pushback on using a name constant everywhere. I'm basically hesitant to add a bunch of process to tests where all the constants are basically already random

Fallout from bytecodealliance#8628 that I forgot to handle.

* Fix some fuzz memory configuration issues Fallout from #8628 that I forgot to handle. * More fuzz tweaks * More tweaks for more bugs

…iance#8628) * Use bytes for maximum size of linear memory with pooling This commit changes configuration of the pooling allocator to use a byte-based unit rather than a page based unit. The previous `PoolingAllocatorConfig::memory_pages` configuration option configures the maximum size that a linear memory may grow to at runtime. This is an important factor in calculation of stripes for MPK and is also a coarse-grained knob apart from `StoreLimiter` to limit memory consumption. This configuration option has been renamed to `max_memory_size` and documented that it's in terms of bytes rather than pages as before. Additionally the documented constraint of `max_memory_size` must be smaller than `static_memory_bound` is now additionally enforced as a minor clean-up as part of this PR as well. * Review comments * Fix benchmark build

* Fix some fuzz memory configuration issues Fallout from bytecodealliance#8628 that I forgot to handle. * More fuzz tweaks * More tweaks for more bugs

alexcrichton requested review from a team as code owners May 15, 2024 17:57

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github-actions bot added fuzzing Issues related to our fuzzing infrastructure wasmtime:api Related to the API of the `wasmtime` crate itself wasmtime:config Issues related to the configuration of Wasmtime labels May 15, 2024

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fitzgen approved these changes May 16, 2024

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alexcrichton added this pull request to the merge queue May 16, 2024

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Fix benchmark build

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alexcrichton requested a review from a team as a code owner May 17, 2024 03:58

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alexcrichton added this pull request to the merge queue May 17, 2024

Merged via the queue into bytecodealliance:main with commit 906ea01 May 17, 2024
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alexcrichton deleted the memory-pages-to-bytes branch May 17, 2024 04:20

alexcrichton added a commit to alexcrichton/wasmtime that referenced this pull request May 17, 2024

Fix some fuzz memory configuration issues

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Fallout from bytecodealliance#8628 that I forgot to handle.

alexcrichton mentioned this pull request May 17, 2024

Fix some fuzz memory configuration issues #8647

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Fix some fuzz memory configuration issues (#8647)

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* Fix some fuzz memory configuration issues Fallout from #8628 that I forgot to handle. * More fuzz tweaks * More tweaks for more bugs

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Use bytes for maximum size of linear memory with pooling #8628

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alexcrichton commented May 16, 2024

		cfg.max_memory32_pages = min / 65536;
		cfg.max_memory64_pages = min / 65535;

Use bytes for maximum size of linear memory with pooling #8628

Use bytes for maximum size of linear memory with pooling #8628

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