lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date:   Fri, 09 Oct 2020 09:47:06 -0700
From:   Chris Goldsworthy <>
Subject: Re: Question regarding ext4_journalled_aops: lack of migrate_page

tOn 2020-10-08 23:42, Chris Goldsworthy wrote:
> Hi there,
> ext4_aops and ext4_da_aops both have a migratepage callback, whereas
> ext4_journalled_aops lacks such a callback.  Why is this so?  I’m
> asking this due to the following: when a page containing EXT4 journal
> buffer heads ends up being migrated, fallback_migrate_page() is used,
> which eventually calls try_to_free_buffers(), which will call
> drop_buffers().  Drop buffers() can fail for a page if that page is on
> the LRU list (see
> Now, if buffer_migrate_page() was supplied as the migratepage callback
> for the journaled aops, this wouldn’t be problem since we ignore the
> LRU lists altogether.
> Resolving this issue will benefit CMA allocations, which might have to
> migrate movable pages that were allocated from a CMA region (the
> assumption is that these pages can be migrated once the memory backing
> these pages is needed).
> Thanks,
> Chris.

An alternative solution to to placing in a migratepage callback is to 
actually remove the buffer heads from an LRU list in drop_buffers() - we 
tried upstreaming such a patch some time ago: .  This would solve the 
problem, and would avoid having to get a migratepage callback for any 
other files systems that have aops without the callback.  This didn't 
get off the ground however, I'm picking up the line of questioning left 
in the previous thread, to determine why EXT4 doesn't have a migratepage 



The Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
a Linux Foundation Collaborative Project

Powered by blists - more mailing lists