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SubjectRe: [PATCH 2/2] proc: meminfo: estimate available memory more conservatively
On Mon 30-11-15 15:00:22, Johannes Weiner wrote:
> The MemAvailable item in /proc/meminfo is to give users a hint of how
> much memory is allocatable without causing swapping, so it excludes
> the zones' low watermarks as unavailable to userspace.
>
> However, for a userspace allocation, kswapd will actually reclaim
> until the free pages hit a combination of the high watermark and the
> page allocator's lowmem protection that keeps a certain amount of DMA
> and DMA32 memory from userspace as well.
>
> Subtract the full amount we know to be unavailable to userspace from
> the number of free pages when calculating MemAvailable.

I am not sure this will make a big or even noticeable difference in the
real life but it makes sense.

>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> fs/proc/meminfo.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
> index 9155a5a..df4661a 100644
> --- a/fs/proc/meminfo.c
> +++ b/fs/proc/meminfo.c
> @@ -57,11 +57,8 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
> /*
> * Estimate the amount of memory available for userspace allocations,
> * without causing swapping.
> - *
> - * Free memory cannot be taken below the low watermark, before the
> - * system starts swapping.
> */
> - available = i.freeram - wmark_low;
> + available = i.freeram - totalreserve_pages;
>
> /*
> * Not all the page cache can be freed, otherwise the system will
> --
> 2.6.2
>
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--
Michal Hocko
SUSE Labs


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