On Tue, May 1, 2012 at 4:26 PM, Anton Vorontsov
<anton.vorontsov@xxxxxxxxxx> wrote:
> This is specially "blended" attribute, the event triggers when kernel
> decides that we're close to the low memory threshold. Userspace should
> not expect very precise meaning of low memory situation, mostly, it's
> just a guess on the kernel's side.
>
> Well, this is the same as userland should not know or care how exactly
> kernel manages the memory, or assume that memory management behaviour
> is a part of the "ABI". So, all the 'low memory' is just guessing, but
> we're trying to do our best. It might be that we will end up with two
> or three variations of 'low memory' thresholds, and all of them would
> be useful for different use cases.
>
> For this implementation, we assume that there's a low memory situation
> for the N pages threshold when we have neither N pages of completely
> free pages, nor we have N reclaimable pages in the cache. This
> effectively means, that if userland expects to allocate N pages, it
> would consume all the free pages, and any further allocations (above
> N) would start draining caches.
>
> In the worst case, prior to hitting the threshold, we might have only
> N pages in cache, and nearly no memory as free pages.
>
> The same 'low memory' meaning is used in the current Android Low
> Memory Killer driver.
>
> Signed-off-by: Anton Vorontsov <anton.vorontsov@xxxxxxxxxx>
I don't see why we couldn't add this. Minchan, thoughts?
> ---
> include/linux/vmevent.h | 7 ++++++
> mm/vmevent.c | 40 ++++++++++++++++++++++++++++++++++
> tools/testing/vmevent/vmevent-test.c | 12 +++++++++-
> 3 files changed, 58 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/vmevent.h b/include/linux/vmevent.h
> index aae0d24..9bfa244 100644
> --- a/include/linux/vmevent.h
> +++ b/include/linux/vmevent.h
> @@ -10,6 +10,13 @@ enum {
> VMEVENT_ATTR_NR_AVAIL_PAGES = 1UL,
> VMEVENT_ATTR_NR_FREE_PAGES = 2UL,
> VMEVENT_ATTR_NR_SWAP_PAGES = 3UL,
> + /*
> + * This is specially blended attribute, the event triggers
> + * when kernel decides that we're close to the low memory threshold.
> + * Don't expect very precise meaning of low memory situation, mostly,
> + * it's just a guess on the kernel's side.
> + */
> + VMEVENT_ATTR_LOWMEM_PAGES = 4UL,
>
> VMEVENT_ATTR_MAX /* non-ABI */
> };
> diff --git a/mm/vmevent.c b/mm/vmevent.c
> index b312236..d278a25 100644
> --- a/mm/vmevent.c
> +++ b/mm/vmevent.c
> @@ -68,10 +68,50 @@ static u64 vmevent_attr_avail_pages(struct vmevent_watch *watch,
> return totalram_pages;
> }
>
> +/*
> + * Here's some implementation details for the "low memory" meaning.
> + *
> + * (The explanation is not in the header file as userland should not
> + * know these details, nor it should assume that the meaning will
> + * always be the same. As well as it should not know how exactly kernel
> + * manages the memory, or assume that memory management behaviour is a
> + * part of the "ABI". So, all the 'low memory' is just guessing, but
> + * we're trying to do our best.)
> + *
> + * For this implementation, we assume that there's a low memory situation
> + * for the N pages threshold when we have neither N pages of completely
> + * free pages, nor we have N reclaimable pages in the cache. This
> + * effectively means, that if userland expects to allocate N pages, it
> + * would consume all the free pages, and any further allocations (above
> + * N) would start draining caches.
> + *
> + * In the worst case, prior hitting the threshold, we might have only
> + * N pages in cache, and nearly no memory as free pages.
> + */
> +static u64 vmevent_attr_lowmem_pages(struct vmevent_watch *watch,
> + struct vmevent_attr *attr)
> +{
> + int free = global_page_state(NR_FREE_PAGES);
> + int file = global_page_state(NR_FILE_PAGES) -
> + global_page_state(NR_SHMEM); /* TODO: account locked pages */
> + int val = attr->value;
> +
> + /*
> + * For convenience we return 0 or attr value (instead of 0/1), it
> + * makes it easier for vmevent_match() to cope with blended
> + * attributes, plus userland might use the value to find out which
> + * threshold triggered.
> + */
> + if (free < val && file < val)
> + return val;
> + return 0;
> +}
> +
> static vmevent_attr_sample_fn attr_samplers[] = {
> [VMEVENT_ATTR_NR_AVAIL_PAGES] = vmevent_attr_avail_pages,
> [VMEVENT_ATTR_NR_FREE_PAGES] = vmevent_attr_free_pages,
> [VMEVENT_ATTR_NR_SWAP_PAGES] = vmevent_attr_swap_pages,
> + [VMEVENT_ATTR_LOWMEM_PAGES] = vmevent_attr_lowmem_pages,
> };
>
> static u64 vmevent_sample_attr(struct vmevent_watch *watch, struct vmevent_attr *attr)
> diff --git a/tools/testing/vmevent/vmevent-test.c b/tools/testing/vmevent/vmevent-test.c
> index fd9a174..c61aed7 100644
> --- a/tools/testing/vmevent/vmevent-test.c
> +++ b/tools/testing/vmevent/vmevent-test.c
> @@ -33,7 +33,7 @@ int main(int argc, char *argv[])
>
> config = (struct vmevent_config) {
> .sample_period_ns = 1000000000L,
> - .counter = 6,
> + .counter = 7,
> .attrs = {
> {
> .type = VMEVENT_ATTR_NR_FREE_PAGES,
> @@ -59,6 +59,13 @@ int main(int argc, char *argv[])
> .type = VMEVENT_ATTR_NR_SWAP_PAGES,
> },
> {
> + .type = VMEVENT_ATTR_LOWMEM_PAGES,
> + .state = VMEVENT_ATTR_STATE_VALUE_LT |
> + VMEVENT_ATTR_STATE_VALUE_EQ |
> + VMEVENT_ATTR_STATE_ONE_SHOT,
> + .value = phys_pages / 2,
> + },
> + {
> .type = 0xffff, /* invalid */
> },
> },
> @@ -108,6 +115,9 @@ int main(int argc, char *argv[])
> case VMEVENT_ATTR_NR_SWAP_PAGES:
> printf(" VMEVENT_ATTR_NR_SWAP_PAGES: %Lu\n", attr->value);
> break;
> + case VMEVENT_ATTR_LOWMEM_PAGES:
> + printf(" VMEVENT_ATTR_LOWMEM_PAGES: %Lu\n", attr->value);
> + break;
> default:
> printf(" Unknown attribute: %Lu\n", attr->value);
> }
> --
> 1.7.9.2
>
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