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<title>[60316] trunk/src/wp-includes/blocks.php: do_blocks(): Free up transient memory leak</title>
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<dt style="float: left; width: 6em; font-weight: bold">Revision</dt> <dd><a style="font-weight: bold" href="https://core.trac.wordpress.org/changeset/60316">60316</a><script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","description":"Review this Commit","action":{"@type":"ViewAction","url":"https://core.trac.wordpress.org/changeset/60316","name":"Review Commit"}}</script></dd>
<dt style="float: left; width: 6em; font-weight: bold">Author</dt> <dd>dmsnell</dd>
<dt style="float: left; width: 6em; font-weight: bold">Date</dt> <dd>2025-06-18 00:49:51 +0000 (Wed, 18 Jun 2025)</dd>
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<pre style='padding-left: 1em; margin: 2em 0; border-left: 2px solid #ccc; line-height: 1.25; font-size: 105%; font-family: sans-serif'>do_blocks(): Free up transient memory leak
There has been a memory inefficiency inside of `do_blocks()` where it
parses the given content then iterates through each top-level block to
render it. Unfortunately each top-level block can considerably add to
the overall memory use involved, and once moving on to the next
top-level block, all of the allocated memory will be retained until the
end of the call to `do_blocks()`.
In this change, each parsed block sub-tree is freed via reset to `null`
after it has been rendered. All top-level blocks are rendered
independently of each other and so this operation is safe - there are no
data dependencies between them.
For a test post of length 2.3 MB containing 138 top-level blocks, this
brought the minimum memory requirement for the PHP process down from
around 450 MB to around 316 MB. This was {U+201C}around{U+201D} since the memory
requirements are non-deterministic and some runs will succeed while
other runs will crash for out-of-memory given the same `memory_limit`.
Impact of this change will be most profound when there exist one or
more top-level blocks which allocate a significant amount of memory
which are not the last top-level-block in a post. This means that
this change might even impact small and typical posts, if the right
blocks are near the start of the post.
Developed in https://github.com/wordpress/wordpress-develop/pull/8999
Discussed in https://core.trac.wordpress.org/ticket/63588
Props dmsnell, joemcgill.
Fixes <a href="https://core.trac.wordpress.org/ticket/63588">#63588</a>.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunksrcwpincludesblocksphp">trunk/src/wp-includes/blocks.php</a></li>
</ul>
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<h3>Diff</h3>
<a id="trunksrcwpincludesblocksphp"></a>
<div class="modfile"><h4 style="background-color: #eee; color: inherit; margin: 1em 0; padding: 1.3em; font-size: 115%">Modified: trunk/src/wp-includes/blocks.php</h4>
<pre class="diff"><span>
<span class="info" style="display: block; padding: 0 10px; color: #888">--- trunk/src/wp-includes/blocks.php 2025-06-18 00:38:50 UTC (rev 60315)
+++ trunk/src/wp-includes/blocks.php 2025-06-18 00:49:51 UTC (rev 60316)
</span><span class="lines" style="display: block; padding: 0 10px; color: #888">@@ -2403,11 +2403,13 @@
</span><span class="cx" style="display: block; padding: 0 10px"> * @return string Updated post content.
</span><span class="cx" style="display: block; padding: 0 10px"> */
</span><span class="cx" style="display: block; padding: 0 10px"> function do_blocks( $content ) {
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- $blocks = parse_blocks( $content );
- $output = '';
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ $blocks = parse_blocks( $content );
+ $top_level_block_count = count( $blocks );
+ $output = '';
</ins><span class="cx" style="display: block; padding: 0 10px">
</span><del style="background-color: #fdd; text-decoration:none; display:block; padding: 0 10px">- foreach ( $blocks as $block ) {
- $output .= render_block( $block );
</del><ins style="background-color: #dfd; text-decoration:none; display:block; padding: 0 10px">+ for ( $i = 0; $i < $top_level_block_count; $i++ ) {
+ $output .= render_block( $blocks[ $i ] );
+ $blocks[ $i ] = null;
</ins><span class="cx" style="display: block; padding: 0 10px"> }
</span><span class="cx" style="display: block; padding: 0 10px">
</span><span class="cx" style="display: block; padding: 0 10px"> // If there are blocks in this content, we shouldn't run wpautop() on it later.
</span></span></pre>
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