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alexfreu's avatar
alexfreu
Copper Contributor
Oct 31, 2019

BrowserMetrics

There is a folder %localappdata%\Microsoft\Edge Dev\User Data\BrowserMetrics with thousands of 4 MB files like BrowserMetrics-5D3A8F5A-1AF0.pma that fill up my precious SSD disk space. Can I remove ...
JimGrisham's avatar
JimGrisham
Iron Contributor
Apr 01, 2021

Alexandra-R (and Edge team devs):

 

Other things of note that I've recently noticed (or heard from others):

 

Spoiler
  1. Edge seems to clean up these files upon launch. It knows how to do that.
  2. Edge behaves differently depending on version
    1. For me, it occurs in:
      1. Edge Stable: Version 89.0.774.63 (Official build) (64-bit)
      2. Edge Canary: Version 91.0.837.0 (Official build) (64-bit)
    2. It does not occur in:
      1. Edge Beta: Version 90.0.818.22 (Official build) beta (64-bit)
    3. Therefore, it seems there is either
      1. a regression between 90.0.918 and 91.0.837, or
      2. a difference in 'feature flag' or other configuration
    4. I did notice that the Beta version ran with the following command line argument that was absent from the Stable version
      1. "--monitor-self"
  3. At first I thought Edge might be losing a 'race condition' with Windows Defender Real Time Protection (RTP); that is, Defender locks the file and Edge can't delete it  (see detail [1] below)
  4. That seems unlikely, though, since the Beta ring works fine with Defender
  5. Instead, it appears that the Stable version (and possibly the Canary one as well) aren't even _trying_ to delete the old files until after the next time Edge is completely closed and re-opened (... which for some people can be hours to weeks!) (see detail [2] below)
  6. Perhaps unrelated, there was a mention of this in one of the file access traces - perhaps it is another lead for the devs:
    1. msedge.dll - RelaunchChromeBrowserWithNewCommandLineIfNeeded

 

 

To recap this entire discussion, it seems there are two (separate but related) issues that need to be fixed:

 

  1. Edge is keeping more than one BrowserMetrics file around, and for far too long
    1. As I understand it, having more than one file in the BrowserMetrics directory is designed to only ever be a short-term (i.e. 30-60 minutes max) occurrence
  2. For some combination of builds/users/conditions, Edge is creating these new files at a very high rate (6-300 files / hour).
    1. Even if the previous issue is corrected, this one is arguably more important and will have more impact on the overall UX of Edge.
    2. Whether or not they are full of data, that can result in a ton of small disk accesses.
      1. Pity those unfortunate students using low-end laptops* with spinning HDDs!
        1. Memory-mapped files like this sometimes get written to very often, since the data is saved in very tiny chunks.
        2. Based on some of the reports from above, one can imagine the poor little hard drive heads bouncing back-and-forth nearly constantly, impacting system responsiveness and the user's overall opinion of Edge
          1. An average laptop HDD may only get 60 operations, likely fewer, each second, for the entire operating system and all applications
          2. The fastest server HDDs still only allow a maximum of about 200 operations / second
        3. As I have previously mentioned (ok, mildly ranted), each new file can drive activity from filesystem, antivirus/Defender, Windows Auditing, disk indexing, and potentially other processes. To the extent that most of these are reads, their biggest negative impact relates to HDDs.
        4. * some customers may even have Windows Virtual Desktop instances backed by HDDs, driven by inertia or Azure budgets
      2. This causes unnecessary wear on consumer SSDs as well.
        1. The primary concern here is with the frequent small disk writes; read cost / wear is fairly insignificant
        2. (I believe Chromium on Android turns this feature off altogether, choosing instead to just keep the data in RAM until it needs to be uploaded.)

 

Thank you for all the attention you and your team are giving to this! :happyface:

 

Happy hunting,

 

  - Jim

 

Detail [1] from item (3) in above list:

Spoiler
  1. Edge creates the 4.0 MiB PMA (Persistent Memory Access) file named "BrowserMetrics-spare.pma" in the "%LocalAppData%\Microsoft\Edge\User Data" directory.
  2. Edge moves that file to the "%LocalAppData%\Microsoft\Edge\User Data\BrowserMetrics" directory and renames it.
  3. Edge loads that re-named file as a memory-mapped file
    1. After some time, the 'spare' file from step 1 is re-created
  4. If Windows Defender is running,
    1. writes to this file are sometimes / always accessed filtered through the Defender (MsMpEng.exe) process (Synchronous Paging I/O)
  5. If Windows Defender ATP (Advanced Threat Protection) is running,
    1. that process (MsSense.exe) requests an 'opportunistic lock (oplock)' [FSCTL_REQUEST_OPLOCK IOCTL (winioctl.h)] while it is scanning
    2. Before that scan is complete (and therefore the oplock is released), Edge (msedge.exe) closes the file

 

Detail [2] from item (5) in above list:

Spoiler
Beta - Version 90.0.818.22 (Official build) beta (64-bit)

  --> Normal (working) process, that prevents build-up of "BrowserMetrics-hhhhhhhh-hhhhh.pma" files:

  CreateFile                                              Desired Access: Generic Read/Write, Disposition: OpenIf, 
                                                            Options: Synchronous IO Non-Alert, Non-Directory File, 
                                                            Attributes: n/a, ShareMode: Read, Write, Delete, 
                                                            AllocationSize: 0, OpenResult: Created
  CreateFileMapping                                       SyncType: SyncTypeCreateSection, 
                                                            PageProtection: PAGE_EXECUTE_READWRITE
                    Result: FILE LOCKED WITH WRITERS
  QueryStandardInformationFile                            AllocationSize: 0, EndOfFile: 0, NumberOfLinks: 1, 
                                                            DeletePending: False, Directory: False
  SetEndOfFileInformationFile                             EndOfFile: 4,194,304
  CreateFileMapping                                       SyncType: SyncTypeOther
  ReadFile                                                Offset: 0, Length: 32,768, I/O Flags: Non-cached, Paging I/O, 
                                                            Synchronous Paging I/O, Priority: Normal
	...
  CreateFile                    IRP_MJ_CREATE
  QueryAttributeTagFile         IRP_MJ_QUERY_INFORMATION  Type: QueryAttributeTagFile, Attributes: AC, ReparseTag: 0x0
  SetDispositionInformationEx   IRP_MJ_SET_INFORMATION    FILE_DISPOSITION_DELETE, FILE_DISPOSITION_POSIX_SEMANTICS, 
                                                            FILE_DISPOSITION_FORCE_IMAGE_SECTION_CHECK
                                IRP_MJ_CLEANUP
  CloseFile                     IRP_MJ_CLOSE
When running the Stable ring version of Edge, "SetDispositionInformationEx" never appears and the files persist.

 

dave260's avatar
dave260
Brass Contributor
Apr 02, 2021
Thanks Jim for all the updates and spoiler alerts! Good information.
I will quickly add at this point, I am using Edge Beta now. It seems to work well, but I haven't tested every possible issue. Interesting that this is the third day I have used Beta, and there is only ONE file in Browser Metrics. This is the third day I have been using it. On the other hand, Stable Edge has 854 BrowserMetric entries for 3/31-4/1 minimal use.
-- Dave

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