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Commit 4db28111 authored by Gerald Schaefer's avatar Gerald Schaefer Committed by Greg Kroah-Hartman
Browse files

s390/gmap: improve THP splitting 



commit ba925fa35057a062ac98c3e8138b013ce4ce351c upstream.

During s390_enable_sie(), we need to take care of splitting all qemu user
process THP mappings. This is currently done with follow_page(FOLL_SPLIT),
by simply iterating over all vma ranges, with PAGE_SIZE increment.

This logic is sub-optimal and can result in a lot of unnecessary overhead,
especially when using qemu and ASAN with large shadow map. Ilya reported
significant system slow-down with one CPU busy for a long time and overall
unresponsiveness.

Fix this by using walk_page_vma() and directly calling split_huge_pmd()
only for present pmds, which greatly reduces overhead.

Cc: <stable@vger.kernel.org> # v5.4+
Reported-by: default avatarIlya Leoshkevich <iii@linux.ibm.com>
Tested-by: default avatarIlya Leoshkevich <iii@linux.ibm.com>
Acked-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: default avatarGerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 756a70b6

arch/s390/mm/gmap.c

+20 −7
Original line number Diff line number Diff line
@@ -2485,23 +2485,36 @@ void gmap_sync_dirty_log_pmd(struct gmap *gmap, unsigned long bitmap[4], 
}

EXPORT_SYMBOL_GPL(gmap_sync_dirty_log_pmd);



#ifdef CONFIG_TRANSPARENT_HUGEPAGE

static int thp_split_walk_pmd_entry(pmd_t *pmd, unsigned long addr,

				    unsigned long end, struct mm_walk *walk)

{

	struct vm_area_struct *vma = walk->vma;



	split_huge_pmd(vma, pmd, addr);

	return 0;

}



static const struct mm_walk_ops thp_split_walk_ops = {

	.pmd_entry	= thp_split_walk_pmd_entry,

};



static inline void thp_split_mm(struct mm_struct *mm)

{

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

	struct vm_area_struct *vma;

	unsigned long addr;



	for (vma = mm->mmap; vma != NULL; vma = vma->vm_next) {

		for (addr = vma->vm_start;

		     addr < vma->vm_end;

		     addr += PAGE_SIZE)

			follow_page(vma, addr, FOLL_SPLIT);

		vma->vm_flags &= ~VM_HUGEPAGE;

		vma->vm_flags |= VM_NOHUGEPAGE;

		walk_page_vma(vma, &thp_split_walk_ops, NULL);

	}

	mm->def_flags |= VM_NOHUGEPAGE;

#endif

}

#else

static inline void thp_split_mm(struct mm_struct *mm)

{

}

#endif /* CONFIG_TRANSPARENT_HUGEPAGE */



/*

 * Remove all empty zero pages from the mapping for lazy refaulting