[notroj]

Two changes for the memory growth reported in httpd PR 70167, where mod_ssl splits a FILE bucket at an offset which is not page-aligned, and the httpd child's memory then grows in proportion to the size of the file sent.

Trunk already page-aligns the offset in apr_mmap_create(), so the growth as reported does not reproduce here; it needs APR 1.7.x with APR-util 1.6.x. Both changes are written to be backported to those branches.

Avoid allocating from the pool when apr_mmap_create() fails

apr_mmap_create() allocated the apr_mmap_t before attempting the mapping, so every failed call left memory in the caller's pool. A FILE bucket retries the mmap for each read, so a persistent failure consumed pool memory for each read of the file. The structure is now allocated only once the file has been mapped, for both the Unix and Windows implementations.

The Windows change has not been compiled or tested.

Read a FILE bucket up to a page boundary before using mmap

A FILE bucket which does not start at a page-aligned offset is now read only as far as the next page boundary, so the remainder is mapped from a page-aligned offset. This applies only if:

• mmap is enabled for the bucket;
• the bucket is larger than the read buffer size, so could not be read in a single read anyway;
• the remainder beyond the page boundary is at least APR_MMAP_THRESHOLD.

The page size comes from sysconf(_SC_PAGESIZE); where that is not available the behaviour is unchanged.

One cost on trunk: a bucket between the read buffer size and APR_MMAP_LIMIT at an unaligned offset was previously a single mmap, and is now one short read followed by one mmap.

Tests

• test_mmap_create_fail (testmmap): a failed apr_mmap_create() does not allocate from the pool. The pool check uses apr_pool_num_bytes(), so it is only effective in a pool-debug build.
• test_mmap_unaligned (testbuckets): a FILE bucket at an unaligned offset, larger than APR_MMAP_LIMIT, is read up to the page boundary and then as MMAP buckets.
• test_mmap_fail (testbuckets): a file which cannot be mapped is read correctly via the fallback path.

The first two fail without the corresponding source change (the first in a pool-debug build). The full test suite passes on Linux x86_64.

Not covered

• Each successfully mapped chunk still leaves one apr_mmap_t in the pool, about 14 bytes per MB read.
• Neither change has been tested on the 1.x branches or end-to-end with httpd.

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