linux-kernel - Re: [External] [PATCH v4] dma-buf: Add DmaBufTotal counter in meminfo

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Message-ID: <CAMZfGtVGvOp4NuAHcVjXB08gfkus+r=iE_oSiWThAXV6zdWBzg@mail.gmail.com>
Date:   Sat, 17 Apr 2021 22:21:13 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Peter Enderborg <Peter.Enderborg@...y.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...e.com>, Neil Brown <neilb@...e.de>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Mike Rapoport <rppt@...nel.org>, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [External] [PATCH v4] dma-buf: Add DmaBufTotal counter in meminfo

On Sat, Apr 17, 2021 at 9:44 PM <Peter.Enderborg@...y.com> wrote:
>
> On 4/17/21 3:07 PM, Muchun Song wrote:
> > On Sat, Apr 17, 2021 at 6:41 PM Peter Enderborg
> > <peter.enderborg@...y.com> 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@...y.com>
> >> ---
> >>  drivers/dma-buf/dma-buf.c | 13 +++++++++++++
> >>  fs/proc/meminfo.c         |  5 ++++-
> >>  include/linux/dma-buf.h   |  1 +
> >>  3 files changed, 18 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> >> index f264b70c383e..197e5c45dd26 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 +1349,16 @@ 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;
> >> +}
> >> +EXPORT_SYMBOL_GPL(dma_buf_allocated_pages);
> > dma_buf_allocated_pages is only called from fs/proc/meminfo.c.
> > I am confused why it should be exported. If it won't be called
> > from the driver module, we should not export it.
>
> Ah. I thought you did not want the GPL restriction. I don't have real
> opinion about it. It's written to be following the rest of the module.
> It is not needed for the usage of dma-buf in kernel module. But I
> don't see any reason for hiding it either.

The modules do not need dma_buf_allocated_pages, hiding it
can prevent the module from calling it. So I think that
EXPORT_SYMBOL_GPL is unnecessary. If one day someone
want to call it from the module, maybe it’s not too late to export
it at that time.

>
>
> > Thanks.
> >
> >> +
> >>  #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
> >>