RESOLVED FIXED314699
[BFCache] Enable MultiProcessBackForwardCache automatically when Site Isolation is active 
https://bugs.webkit.org/show_bug.cgi?id=314699
Summary [BFCache] Enable MultiProcessBackForwardCache automatically when Site Isolati...
Basuke Suzuki
Reported 2026-05-12 20:55:04 PDT
Followup to multi-process BFCache work (tracking patch bug 313657). The MultiProcessBackForwardCacheEnabled preference — described as "Enable back/forward cache when site isolation is active" — currently defaults to false and must be toggled on independently from SiteIsolationEnabled. In practice the two features are intended to be used together; under Site Isolation, BFCache requires the UIProcess coordination that this flag unlocks, and the admission check in BackForwardCache::addIfCacheable already rejects any SI page when the flag is off. Auto-enable MultiProcessBackForwardCacheEnabled at page creation time whenever SiteIsolationEnabled is on, mirroring the existing pattern for UseUIProcessForBackForwardItemLoading in Source/WebKit/UIProcess/WebProcessPool.cpp (around the 'if (siteIsolationEnabled) ...' block near line 1339). Also clean up redundant enableFeature(... MultiProcessBackForwardCacheEnabled ...) calls in SiteIsolation.mm API tests, and update any Layout / API test expectations that shift because BFCache is now active by default under SI. rdar://176944362
Attachments
Add attachment proposed patch, testcase, etc.
Basuke Suzuki
Comment 1 2026-05-13 07:25:18 PDT
Pull request: https://github.com/WebKit/WebKit/pull/64839
Basuke Suzuki
Comment 2 2026-05-21 12:02:25 PDT
Pull request: https://github.com/WebKit/WebKit/pull/65426
EWS
Comment 3 2026-06-03 17:54:59 PDT
Committed 314514@main (c69c4853e6d2): <https://commits.webkit.org/314514@main> Reviewed commits have been landed. Closing PR #64839 and removing active labels.
Note You need to log in before you can comment on or make changes to this bug.