lkml.org 
[lkml]   [2005]   [May]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [openib-general] Re: [PATCH][RFC][0/4] InfiniBand userspace verbs implementation
On 5/7/05, Hugh Dickins <hugh@veritas.com> wrote:
> > My understanding is that mlock() could in theory allow the page to be moved,
> > but that currently nothing in the kernel would actually move it. However,
> > that could change in the future to allow hot-swapping of RAM.
>
> That's my understanding too, that nothing currently does so. Aside from
> hot-swapping RAM, there's also a need to be able to migrate pages around
> RAM, either to unfragment memory allowing higher-order allocations to
> succeed more often, or to get around extreme dmamem/normal-mem/highmem
> imbalances without dedicating huge reserves. Those would more often
> succeed if uninhibited by mlock.

Hugh,

If I am reading you correctly, you are saying that mlock currently
prevents pages from migrating around to unfragment memory, but
get_user_pages does not prevent this? If this is the case, this could
very easily be the problem Timur was experiencing. He is using
get_user_pages to lock pages long term (for the life of the process,
beyond the bounds of a single system call).

If it is possible for a page to be migrated in physical memory during
extreme virtual memory pressure while the reference count is held with
get_user_pages, that would cause the problem where the hardware is no
longer mapped to the same page as the application.

BTW: In earlier kernels, I experienced the same issues in our IB
drivers when trying to pin pages using only get_user_pages.

--
Bill Jordan
InfiniCon Systems
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-05-11 22:16    [W:0.108 / U:1.788 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site