Bug 167468 – Web Inspector: iOS: Memory timeline shows impossible values for Page size (underflowed)

• Status: RESOLVED
• Resolution: FIXED
• Component: Web Inspector

[Joseph Pecoraro]

Summary:
iOS: Memory timeline shows impossible values for Page size (underflowed)

Steps to Reproduce:
1. Inspect iOS 10 device
2. Enable Memory Timeline
3. Start and stop timeline recording
  => Page memory values are impossible

Notes:
- vmPageSize() is returning 0 on iOS (sandbox violation prevents accessing sysctlbyname)

[Joseph Pecoraro]

<rdar://problem/30099051>

[Joseph Pecoraro]

This developer forum post seems to offer the most accurate information:
https://forums.developer.apple.com/thread/47532

Namely:

These should all match:

  - getpagesize
  - sysconf(_SC_PAGESIZE)
  - vm_page_size

As:

  • 16 KiB on 64-bit ARM platforms
  • 4 KiB on everything else

However, "various low-level Mach APIs (which we are using here) continue to work in terms of 4 KiB pages."  You can get that value using vm_kernel_page_size.

---

So this ends up matching bmalloc's vmPageSizePhysical():

> inline size_t vmPageSizePhysical()
> {
> #if (BPLATFORM(IOS) && __IPHONE_OS_VERSION_MIN_REQUIRED >= 100000)
>     return vm_kernel_page_size;
> #else
>     static size_t cached;
>     if (!cached)
>         cached = sysconf(_SC_PAGESIZE);
>     return cached;
> #endif
> }

[Joseph Pecoraro]

Created attachment 299862 [details]
[PATCH] Proposed Fix

[Andreas Kling]

Comment on attachment 299862 [details]
[PATCH] Proposed Fix

r=me!

[WebKit Commit Bot]

Comment on attachment 299862 [details]
[PATCH] Proposed Fix

Clearing flags on attachment: 299862

Committed r211241: <http://trac.webkit.org/changeset/211241>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.