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Date: Thu, 18 Feb 2016 19:19:09 +0900 From: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> To: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> Cc: Joonsoo Kim <js1304@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Minchan Kim <minchan@...nel.org>, Linux Memory Management List <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, Sergey Senozhatsky <sergey.senozhatsky@...il.com> Subject: Re: [RFC PATCH 3/3] mm/zsmalloc: change ZS_MAX_PAGES_PER_ZSPAGE On (02/18/16 18:55), Sergey Senozhatsky wrote: > > There is a reason that it is order of 2. Increasing ZS_MAX_PAGES_PER_ZSPAGE > > is related to ZS_MIN_ALLOC_SIZE. If we don't have enough OBJ_INDEX_BITS, > > ZS_MIN_ALLOC_SIZE would be increase and it causes regression on some > > system. > > Thanks! > > do you mean PHYSMEM_BITS != BITS_PER_LONG systems? PAE/LPAE? isn't it > the case that on those systems ZS_MIN_ALLOC_SIZE already bigger than 32? I mean, yes, there are ZS_ALIGN requirements that I completely ignored, thanks for pointing that out. just saying, not insisting on anything, theoretically, trading 32 bit size objects in exchange of reducing a much bigger memory wastage is sort of interesting. zram stores objects bigger than 3072 as huge objects, leaving 4096-3072 bytes unused, and it'll take 4096-3072/32 = 4000 32 bit objects to beat that single 'bad' compression object in storing inefficiency... well, patches 0001/0002 are trying to address this a bit, but the biggest problem is still there: we have too many ->huge classes and they are a bit far from good. -ss
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