Re: Re: mm/zsmalloc.c: count in handle's size when calculating pages_per_zspage

[Yinghao Xie]

> > From 159d74b5a8f3d0f07e18ddad74b7025cf17dcc69 Mon Sep 17 00:00:00
> 2001
> > From: Yinghao Xie <yinghao.xie@xxxxxxxxxxx>
> > Date: Thu, 19 Mar 2015 19:32:25 +0800
> > Subject: [PATCH] mm/zsmalloc.c: count in handle's size when
> > calculating  size_class's pages_per_zspage
> >
> > 1. Fix wastage calculation;
> > 2. Indirect handle introduced extra ZS_HANDLE_SIZE size for each
> object,it's transparent
> >    for upper function, but a size_class's total objects will changed:
> >    take the 43rd class which class_size = 32 + 43 * 16 = 720 as example:
> > 	4096 * 1 % 720 = 496
> > 	4096 * 2 % 720 = 272
> > 	4096 * 3 % 720 = 48
> > 	4096 * 4 %720 = 544
> >    after handle introduced,class_size + ZS_HANDLE_SIZE (4 on 32bit) = 724
> > 	4096 * 1 % 724 = 476
> > 	4096 * 2 % 724 = 228
> > 	4096 * 3 % 724 = 704
> > 	4096 * 4 % 724 = 456
> >     Clearly, ZS_HANDLE_SIZE should be considered when calculating
> > pages_per_zspage;
> 
> Zsmalloc adds ZS_SIZE_HANDLE to size user passed before getting size_class
> so we don't need to change size_class to calculate optimal pages for zspage.
> 

I read code agian,and agreed with you,it is my misunderstanding

> >
> > 3. in get_size_class_index(), min(zs_size_classes - 1, idx) insures a huge
> class's
> >    index <= zs_size_classes - 1, so it's no need to check again;
> 
> Sorry, I don't get it, either.
>
ditto, my fault,sorry 
 
> >
> > Signed-off-by: Yinghao Xie <yinghao.xie@xxxxxxxxxxx>
> > ---
> >  mm/zsmalloc.c |   15 ++++++---------
> >  1 file changed, 6 insertions(+), 9 deletions(-)
> >
> > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 461243e..64c379b
> > 100644
> > --- a/mm/zsmalloc.c
> > +++ b/mm/zsmalloc.c
> > @@ -760,7 +760,8 @@ out:
> >   * to form a zspage for each size class. This is important
> >   * to reduce wastage due to unusable space left at end of
> >   * each zspage which is given as:
> > - *	wastage = Zp - Zp % size_class
> > + *	wastage = Zp % (class_size + ZS_HANDLE_SIZE)
> > + *	usage = Zp - wastage
> >   * where Zp = zspage size = k * PAGE_SIZE where k = 1, 2, ...
> >   *
> >   * For example, for size class of 3/8 * PAGE_SIZE, we should @@
> > -773,6 +774,9 @@ static int get_pages_per_zspage(int class_size)
> >  	/* zspage order which gives maximum used size per KB */
> >  	int max_usedpc_order = 1;
> >
> > +	if (class_size > ZS_MAX_ALLOC_SIZE)
> > +		class_size = ZS_MAX_ALLOC_SIZE;
> > +
> >  	for (i = 1; i <= ZS_MAX_PAGES_PER_ZSPAGE; i++) {
> >  		int zspage_size;
> >  		int waste, usedpc;
> > @@ -1426,11 +1430,6 @@ unsigned long zs_malloc(struct zs_pool *pool,
> size_t size)
> >  	/* extra space in chunk to keep the handle */
> >  	size += ZS_HANDLE_SIZE;
> >  	class = pool->size_class[get_size_class_index(size)];
> > -	/* In huge class size, we store the handle into first_page->private */
> > -	if (class->huge) {
> > -		size -= ZS_HANDLE_SIZE;
> > -		class = pool->size_class[get_size_class_index(size)];
> > -	}
> >
> >  	spin_lock(&class->lock);
> >  	first_page = find_get_zspage(class); @@ -1856,9 +1855,7 @@ struct
> > zs_pool *zs_create_pool(char *name, gfp_t flags)
> >  		struct size_class *class;
> >
> >  		size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
> > -		if (size > ZS_MAX_ALLOC_SIZE)
> > -			size = ZS_MAX_ALLOC_SIZE;
> > -		pages_per_zspage = get_pages_per_zspage(size);
> > +		pages_per_zspage = get_pages_per_zspage(size +
> ZS_HANDLE_SIZE);
> >
> >  		/*
> >  		 * size_class is used for normal zsmalloc operation such
> > --
> > 1.7.9.5