No objections?
Then I assume this is OK...
Helge
On 04/17/2014 10:45 PM, Helge Deller wrote:
> Would the following patch be acceptable?
> It adds an additional field to struct address_space which will most likely only
> be used by the parisc arch.
>
> If it's acceptable, I would like to push it through the parisc tree, if not,
> I'm of course open to other ideas too.
>
> Thanks,
> Helge
>
> PATCH:
> [RFC,PATCH] mm,parisc: keep track of last mmap'ed address
>
> Because of parisc's cache aliasing constraints we need to map shared pages at a
> multiple of 4MB while most other architectures can map files at any multiple of
> PAGE_SIZE. In the past this constraint was ensured by calculating a virtual
> offset into this 4MB region which is based on the physical address of the
> kernel mapping variable (right-shift value of filp->f_mapping by 8 bits).
> Since we only have a 32bit userspace (even when running on a 64bit kernel) this
> often leads to large gaps in the maps of the userspace processes and to out of
> memory situations even if physical memory was still free. Of course I did
> played with other variants of shifting the f_mapping value to find better
> offsets but this didn't helped either.
>
> This patch chooses a different approach.
> It adds the additional field i_mmap_lastmmap to the address_space struct to
> keep track of the last mapping of a shared file. With this bookkeeping it's
> possible for the parisc memory allocator to
> a) choose a new mapping offset if the file hasn't been mapped yet, and
> b) take the last-used mapping if it was already mapped by another process.
>
> Overall this approach leads to a more condensed memory usage on parisc because
> the shared files will now be mapped much closer to each other. This is e.g.
> visible with shared libraries which are now not any longer cluttered around
> in the userspace process but close to each other at the top of the userspace
> memory.
>
> Signed-off-by: Helge Deller <deller@xxxxxx>
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 81048f9..f757a5c 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -416,6 +416,9 @@ struct address_space {
> unsigned int i_mmap_writable;/* count VM_SHARED mappings */
> struct rb_root i_mmap; /* tree of private and shared mappings */
> struct list_head i_mmap_nonlinear;/*list VM_NONLINEAR mappings */
> +#ifdef CONFIG_MMAP_TRACKING
> + unsigned long i_mmap_lastmmap; /* address of last mmap */
> +#endif
> struct mutex i_mmap_mutex; /* protect tree, count, list */
> /* Protected by tree_lock together with the radix tree */
> unsigned long nrpages; /* number of total pages */
> diff --git a/mm/mmap.c b/mm/mmap.c
> index b1202cf..e2659c3 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -212,8 +212,13 @@ static void __remove_shared_vm_struct(struct vm_area_struct *vma,
> {
> if (vma->vm_flags & VM_DENYWRITE)
> atomic_inc(&file_inode(file)->i_writecount);
> - if (vma->vm_flags & VM_SHARED)
> + if (vma->vm_flags & VM_SHARED) {
> mapping->i_mmap_writable--;
> +#ifdef CONFIG_MMAP_TRACKING
> + if (mapping->i_mmap_writable == 0)
> + mapping->i_mmap_lastmmap = 0;
> +#endif
> + }
>
> flush_dcache_mmap_lock(mapping);
> if (unlikely(vma->vm_flags & VM_NONLINEAR))
> diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
> index bb2a8ec..9518361 100644
> --- a/arch/parisc/Kconfig
> +++ b/arch/parisc/Kconfig
> @@ -38,6 +38,9 @@ config PARISC
> config MMU
> def_bool y
>
> +config MMAP_TRACKING
> + def_bool y
> +
> config STACK_GROWSUP
> def_bool y
>
> diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
> index 31ffa9b..7d8cbd1 100644
> --- a/arch/parisc/kernel/sys_parisc.c
> +++ b/arch/parisc/kernel/sys_parisc.c
> @@ -36,12 +36,12 @@
> #include <linux/personality.h>
> #include <linux/random.h>
>
> -/* we construct an artificial offset for the mapping based on the physical
> - * address of the kernel mapping variable */
> +/* the address_space struct holds a field i_mmap_lastmmap with the last mapping
> + * of this file for us */
> #define GET_LAST_MMAP(filp) \
> - (filp ? ((unsigned long) filp->f_mapping) >> 8 : 0UL)
> + (filp ? filp->f_mapping->i_mmap_lastmmap : 0UL)
> #define SET_LAST_MMAP(filp, val) \
> - { /* nothing */ }
> + { if (filp) filp->f_mapping->i_mmap_lastmmap = (val); }
>
> static int get_offset(unsigned int last_mmap)
> {
--
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