Messages in this thread | | | Date | Thu, 14 Jul 2022 16:20:17 +0300 | Subject | Re: [PATCH v4 1/1] Create debugfs file with virtio balloon usage information | From | Alexander Atanasov <> |
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Hello,
On 14/07/2022 14:35, David Hildenbrand wrote: > On 05.07.22 10:36, Alexander Atanasov wrote: >> Allow the guest to know how much it is ballooned by the host. >> It is useful when debugging out of memory conditions. >> >> When host gets back memory from the guest it is accounted >> as used memory in the guest but the guest have no way to know >> how much it is actually ballooned. >> >> Signed-off-by: Alexander Atanasov <alexander.atanasov@virtuozzo.com> >> --- >> drivers/virtio/virtio_balloon.c | 77 +++++++++++++++++++++++++++++ >> include/uapi/linux/virtio_balloon.h | 1 + >> 2 files changed, 78 insertions(+) >> >> V2: >> - fixed coding style >> - removed pretty print >> V3: >> - removed dublicate of features >> - comment about balooned_pages more clear >> - convert host pages to balloon pages >> V4: >> - added a define for BALLOON_PAGE_SIZE to make things clear >> >> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c >> index b9737da6c4dd..dc4ad584b947 100644 >> --- a/drivers/virtio/virtio_balloon.c >> +++ b/drivers/virtio/virtio_balloon.c >> @@ -10,6 +10,7 @@ >> #include <linux/virtio_balloon.h> >> #include <linux/swap.h> >> #include <linux/workqueue.h> >> +#include <linux/debugfs.h> >> #include <linux/delay.h> >> #include <linux/slab.h> >> #include <linux/module.h> >> @@ -731,6 +732,77 @@ static void report_free_page_func(struct work_struct *work) >> } >> } >> >> +/* >> + * DEBUGFS Interface >> + */ >> +#ifdef CONFIG_DEBUG_FS >> + >> +#define guest_to_balloon_pages(i) ((i)*VIRTIO_BALLOON_PAGES_PER_PAGE) >> +/** >> + * virtio_balloon_debug_show - shows statistics of balloon operations. >> + * @f: pointer to the &struct seq_file. >> + * @offset: ignored. >> + * >> + * Provides the statistics that can be accessed in virtio-balloon in the debugfs. >> + * >> + * Return: zero on success or an error code. >> + */ >> + >> +static int virtio_balloon_debug_show(struct seq_file *f, void *offset) >> +{ >> + struct virtio_balloon *b = f->private; >> + u32 num_pages; >> + struct sysinfo i; >> + >> + si_meminfo(&i); >> + >> + seq_printf(f, "%-22s: %d\n", "page_size", VIRTIO_BALLOON_PAGE_SIZE); >> + >> + virtio_cread_le(b->vdev, struct virtio_balloon_config, actual, >> + &num_pages); >> + /* >> + * Pages allocated by host from the guest memory. >> + * Host inflates the balloon to get more memory. >> + * Guest needs to deflate the balloon to get more memory. >> + */ > Please drop that comment. This is basic virtio-balloon operation that > must not be explained at this point.
Ok
>> + seq_printf(f, "%-22s: %u\n", "ballooned_pages", num_pages); >> + >> + /* Total Memory for the guest from host */ >> + seq_printf(f, "%-22s: %lu\n", "total_pages", >> + guest_to_balloon_pages(i.totalram)); > totalram is calculated from totalram_pages(). > > When we inflate/deflate, we adjust totalram as well via > adjust_managed_page_count().
That is true only when not using DEFLATE_ON_OOM.
Otherwise inflated memory is accounted as used and total ram stays the same. > Consequently, this doesn't calculate what you actually want? > Total memory would be totalram+inflated, current would be totalram.
My calculations are correct for the case deflate_on_oom is enabled.
> But, TBH, only export num_pages. User space can just lookup the other > information (totalram) via /proc/meminfo.
I have missed that the memory accounting is made differently depending on a flag.
Since the calculations are different i'd prefer to have the values calculate and printed there.
Where no matter what the flags is:
- ballooned_pages -> how much is balloon inflated - total_pages -> total ram the guest can get - current_pages -> current ram the guest have
Patch to unify both cases with or without deflate on oom coming next.
--
Regards, Alexander Atanasov
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