On 19 Aug 2018, at 23:22, Andrea Arcangeli wrote:
<snip>
>
> Reported-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> ---
> include/linux/gfp.h | 18 ++++++++++++++++++
> mm/mempolicy.c | 12 +++++++++++-
> mm/page_alloc.c | 4 ++++
> 3 files changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index a6afcec53795..3c04d5d90e6d 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -44,6 +44,7 @@ struct vm_area_struct;
> #else
> #define ___GFP_NOLOCKDEP 0
> #endif
> +#define ___GFP_ONLY_COMPACT 0x1000000u
> /* If the above are modified, __GFP_BITS_SHIFT may need updating */
>
> /*
> @@ -178,6 +179,21 @@ struct vm_area_struct;
> * definitely preferable to use the flag rather than opencode endless
> * loop around allocator.
> * Using this flag for costly allocations is _highly_ discouraged.
> + *
> + * __GFP_ONLY_COMPACT: Only invoke compaction. Do not try to succeed
> + * the allocation by freeing memory. Never risk to free any
> + * "PAGE_SIZE" memory unit even if compaction failed specifically
> + * because of not enough free pages in the zone. This only makes sense
> + * only in combination with __GFP_THISNODE (enforced with a
> + * VM_WARN_ON), to restrict the THP allocation in the local node that
> + * triggered the page fault and fallback into PAGE_SIZE allocations in
> + * the same node. We don't want to invoke reclaim because there may be
> + * plenty of free memory already in the local node. More importantly
> + * there may be even plenty of free THP available in remote nodes so
> + * we should allocate those if something instead of reclaiming any
> + * memory in the local node. Implementation detail: set ___GFP_NORETRY
> + * too so that ___GFP_ONLY_COMPACT only needs to be checked in a slow
> + * path.
> */
> #define __GFP_IO ((__force gfp_t)___GFP_IO)
> #define __GFP_FS ((__force gfp_t)___GFP_FS)
> @@ -187,6 +203,8 @@ struct vm_area_struct;
> #define __GFP_RETRY_MAYFAIL ((__force gfp_t)___GFP_RETRY_MAYFAIL)
> #define __GFP_NOFAIL ((__force gfp_t)___GFP_NOFAIL)
> #define __GFP_NORETRY ((__force gfp_t)___GFP_NORETRY)
> +#define __GFP_ONLY_COMPACT ((__force gfp_t)(___GFP_NORETRY | \
> + ___GFP_ONLY_COMPACT))
>
> /*
> * Action modifiers
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index d6512ef28cde..6bf839f20dcc 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2047,8 +2047,18 @@ alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
>
> if (!nmask || node_isset(hpage_node, *nmask)) {
> mpol_cond_put(pol);
> + /*
> + * We restricted the allocation to the
> + * hpage_node so we must use
> + * __GFP_ONLY_COMPACT to allow at most a
> + * compaction attempt and not ever get into
> + * reclaim or it'll swap heavily with
> + * transparent_hugepage/defrag = always (or
> + * madvise under MADV_HUGEPAGE).
> + */
> page = __alloc_pages_node(hpage_node,
> - gfp | __GFP_THISNODE, order);
> + gfp | __GFP_THISNODE |
> + __GFP_ONLY_COMPACT, order);
> goto out;
> }
> }
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index a790ef4be74e..01a5c2bd0860 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4144,6 +4144,10 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> */
> if (compact_result == COMPACT_DEFERRED)
> goto nopage;
> + if (gfp_mask & __GFP_ONLY_COMPACT) {
> + VM_WARN_ON(!(gfp_mask & __GFP_THISNODE));
> + goto nopage;
> + }
>
> /*
> * Looks like reclaim/compaction is worth trying, but
I think this can also be triggered in khugepaged. In collapse_huge_page(), khugepaged_alloc_page()
would also cause DIRECT_RECLAIM if defrag==always, since GFP_TRANSHUGE implies __GFP_DIRECT_RECLAIM.
But is it an expected behavior of khugepaged?
—
Best Regards,
Yan Zi
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