Re: [PATCH 2/2] mm: add a field to store names for private anonymous memory

[Pekka Enberg <penberg@kernel.org>]

On 07/12/2013 05:34 AM, Colin Cross wrote:
> Userspace processes often have multiple allocators that each do
> anonymous mmaps to get memory.  When examining memory usage of
> individual processes or systems as a whole, it is useful to be
> able to break down the various heaps that were allocated by
> each layer and examine their size, RSS, and physical memory
> usage.
>
> This patch adds a user pointer to the shared union in
> vm_area_struct that points to a null terminated string inside
> the user process containing a name for the vma.  vmas that
> point to the same address will be merged, but vmas that
> point to equivalent strings at different addresses will
> not be merged.
>
> Userspace can set the name for a region of memory by calling
> prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, start, len, (unsigned long)name);
> Setting the name to NULL clears it.
>
> The names of named anonymous vmas are shown in /proc/pid/maps
> as [anon:<name>] and in /proc/pid/smaps in a new "Name" field
> that is only present for named vmas.  If the userspace pointer
> is no longer valid all or part of the name will be replaced
> with "<fault>".
>
> The idea to store a userspace pointer to reduce the complexity
> within mm (at the expense of the complexity of reading
> /proc/pid/mem) came from Dave Hansen.  This results in no
> runtime overhead in the mm subsystem other than comparing
> the anon_name pointers when considering vma merging.  The pointer
> is stored in a union with fieds that are only used on file-backed
> mappings, so it does not increase memory usage.
>
> Signed-off-by: Colin Cross <ccross@android.com>

So how does this perform if I do prctl(PR_SET_VMA_ANON_NAME)
for thousands of relatively small (max 1 KB) JIT generated
functions? Will we run into MM problems because the VMAs are
not mergeable?

			Pekka

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>