[Webkit-unassigned] [Bug 226122] New: [bmalloc] Rollout r276266 because WebKit processes are spending much more time in madvise

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=226122

            Bug ID: 226122
           Summary: [bmalloc] Rollout r276266 because WebKit processes are
                    spending much more time in madvise
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: msaboff at apple.com

The change for https://bugs.webkit.org/show_bug.cgi?id=224706 causes more calls to madvise.  The way that the bmalloc scavenger calls madvise(..., MADV_FREE_REUSABLE) to decommit ranges is conservative, in that it merges free pages with adjacent free pages.  When we decommit via madvise(), we decommit the whole free range, including pages that have already been decomitted.  Rolling out r276266 to do some automated testing.  At the same time, we'll work on changing the madvise() decommitting to be more precise.

Note that the committing of pages by calling madvise(..., MADV_FREE_REUSE), making them available for bmalloc to use, is precise.  We only call it when are going to use the pages in the range.

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