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    SubjectRe: [PATCH v5] dma-buf: Add DmaBufTotal counter in meminfo
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    On 4/20/21 1:14 PM, Daniel Vetter wrote:
    > On Tue, Apr 20, 2021 at 09:26:00AM +0000, Peter.Enderborg@sony.com wrote:
    >> On 4/20/21 10:58 AM, Daniel Vetter wrote:
    >>> On Sat, Apr 17, 2021 at 06:38:35PM +0200, Peter Enderborg wrote:
    >>>> This adds a total used dma-buf memory. Details
    >>>> can be found in debugfs, however it is not for everyone
    >>>> and not always available. dma-buf are indirect allocated by
    >>>> userspace. So with this value we can monitor and detect
    >>>> userspace applications that have problems.
    >>>>
    >>>> Signed-off-by: Peter Enderborg <peter.enderborg@sony.com>
    >>> So there have been tons of discussions around how to track dma-buf and
    >>> why, and I really need to understand the use-cass here first I think. proc
    >>> uapi is as much forever as anything else, and depending what you're doing
    >>> this doesn't make any sense at all:
    >>>
    >>> - on most linux systems dma-buf are only instantiated for shared buffer.
    >>> So there this gives you a fairly meaningless number and not anything
    >>> reflecting gpu memory usage at all.
    >>>
    >>> - on Android all buffers are allocated through dma-buf afaik. But there
    >>> we've recently had some discussions about how exactly we should track
    >>> all this, and the conclusion was that most of this should be solved by
    >>> cgroups long term. So if this is for Android, then I don't think adding
    >>> random quick stop-gaps to upstream is a good idea (because it's a pretty
    >>> long list of patches that have come up on this).
    >>>
    >>> So what is this for?
    >> For the overview. dma-buf today only have debugfs for info. Debugfs
    >> is not allowed by google to use in andoid. So this aggregate the information
    >> so we can get information on what going on on the system. 
    >>
    >> And the LKML standard respond to that is "SHOW ME THE CODE".
    > Yes. Except this extends to how exactly this is supposed to be used in
    > userspace and acted upon.
    >
    >> When the top memgc has a aggregated information on dma-buf it is maybe
    >> a better source to meminfo. But then it also imply that dma-buf requires memcg.
    >>
    >> And I dont see any problem to replace this with something better with it is ready.
    > The thing is, this is uapi. Once it's merged we cannot, ever, replace it.
    > It must be kept around forever, or a very close approximation thereof. So
    > merging this with the justification that we can fix it later on or replace
    > isn't going to happen.

    It is intended to be relevant as long there is a dma-buf. This is a proper
    metric. If the newer implementations is not get the same result it is
    not doing it right and is not better. If a memcg counter or a global_zone
    counter do the same thing they it can replace the suggested method.

    But I dont think they will. dma-buf does not have to be mapped to a process,
    and the case of vram, it is not covered in current global_zone. All of them
    would be very nice to have in some form. But it wont change what the
    correct value of what "Total" is.


    > -Daniel
    >
    >>> -Daniel
    >>>
    >>>> ---
    >>>> drivers/dma-buf/dma-buf.c | 12 ++++++++++++
    >>>> fs/proc/meminfo.c | 5 ++++-
    >>>> include/linux/dma-buf.h | 1 +
    >>>> 3 files changed, 17 insertions(+), 1 deletion(-)
    >>>>
    >>>> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
    >>>> index f264b70c383e..4dc37cd4293b 100644
    >>>> --- a/drivers/dma-buf/dma-buf.c
    >>>> +++ b/drivers/dma-buf/dma-buf.c
    >>>> @@ -37,6 +37,7 @@ struct dma_buf_list {
    >>>> };
    >>>>
    >>>> static struct dma_buf_list db_list;
    >>>> +static atomic_long_t dma_buf_global_allocated;
    >>>>
    >>>> static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen)
    >>>> {
    >>>> @@ -79,6 +80,7 @@ static void dma_buf_release(struct dentry *dentry)
    >>>> if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
    >>>> dma_resv_fini(dmabuf->resv);
    >>>>
    >>>> + atomic_long_sub(dmabuf->size, &dma_buf_global_allocated);
    >>>> module_put(dmabuf->owner);
    >>>> kfree(dmabuf->name);
    >>>> kfree(dmabuf);
    >>>> @@ -586,6 +588,7 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
    >>>> mutex_lock(&db_list.lock);
    >>>> list_add(&dmabuf->list_node, &db_list.head);
    >>>> mutex_unlock(&db_list.lock);
    >>>> + atomic_long_add(dmabuf->size, &dma_buf_global_allocated);
    >>>>
    >>>> return dmabuf;
    >>>>
    >>>> @@ -1346,6 +1349,15 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, struct dma_buf_map *map)
    >>>> }
    >>>> EXPORT_SYMBOL_GPL(dma_buf_vunmap);
    >>>>
    >>>> +/**
    >>>> + * dma_buf_allocated_pages - Return the used nr of pages
    >>>> + * allocated for dma-buf
    >>>> + */
    >>>> +long dma_buf_allocated_pages(void)
    >>>> +{
    >>>> + return atomic_long_read(&dma_buf_global_allocated) >> PAGE_SHIFT;
    >>>> +}
    >>>> +
    >>>> #ifdef CONFIG_DEBUG_FS
    >>>> static int dma_buf_debug_show(struct seq_file *s, void *unused)
    >>>> {
    >>>> diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
    >>>> index 6fa761c9cc78..ccc7c40c8db7 100644
    >>>> --- a/fs/proc/meminfo.c
    >>>> +++ b/fs/proc/meminfo.c
    >>>> @@ -16,6 +16,7 @@
    >>>> #ifdef CONFIG_CMA
    >>>> #include <linux/cma.h>
    >>>> #endif
    >>>> +#include <linux/dma-buf.h>
    >>>> #include <asm/page.h>
    >>>> #include "internal.h"
    >>>>
    >>>> @@ -145,7 +146,9 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
    >>>> show_val_kb(m, "CmaFree: ",
    >>>> global_zone_page_state(NR_FREE_CMA_PAGES));
    >>>> #endif
    >>>> -
    >>>> +#ifdef CONFIG_DMA_SHARED_BUFFER
    >>>> + show_val_kb(m, "DmaBufTotal: ", dma_buf_allocated_pages());
    >>>> +#endif
    >>>> hugetlb_report_meminfo(m);
    >>>>
    >>>> arch_report_meminfo(m);
    >>>> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
    >>>> index efdc56b9d95f..5b05816bd2cd 100644
    >>>> --- a/include/linux/dma-buf.h
    >>>> +++ b/include/linux/dma-buf.h
    >>>> @@ -507,4 +507,5 @@ int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *,
    >>>> unsigned long);
    >>>> int dma_buf_vmap(struct dma_buf *dmabuf, struct dma_buf_map *map);
    >>>> void dma_buf_vunmap(struct dma_buf *dmabuf, struct dma_buf_map *map);
    >>>> +long dma_buf_allocated_pages(void);
    >>>> #endif /* __DMA_BUF_H__ */
    >>>> --
    >>>> 2.17.1
    >>>>
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