On Thu, 18 Dec 2008 10:47:50 +0300 Yuri Tikhonov <y...@emcraft.com> wrote:
> Hello Paul, > > On Friday 12 December 2008 03:48, Paul Mackerras wrote: > > Andrew Morton writes: > > > > > > +#if (8 * THREAD_SIZE) > PAGE_SIZE > > > > max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE); > > > > +#else > > > > + max_threads = mempages * (PAGE_SIZE / (8 * THREAD_SIZE)); > > > > +#endif > > > > > > The expression you've chosen here can be quite inacccurate, because > > > ((PAGE_SIZE / (8 * THREAD_SIZE)) is a small number. The way to > > > preserve accuracy is > > > > The assumption is that THREAD_SIZE is a power of 2, as is PAGE_SIZE. > > > > I think Yuri should be increasing THREAD_SIZE for the larger page > > sizes he's implementing, because we have on-stack arrays whose size > > depends on the page size. I suspect that having THREAD_SIZE less than > > 1/8 of PAGE_SIZE risks stack overflows, and the better fix is for Yuri > > to make sure THREAD_SIZE is at least 1/8 of PAGE_SIZE. (In fact, more > > may be needed - someone should work out what fraction is actually > > needed.) > > Right, thanks for pointing this. I guess, I was just lucky since didn't run > into > problems with stack overflows. So, I agree that we should increase the > THREAD_SIZE in case of 256KB pages up to 1/8 of PAGE_SIZE, that is up > to 32KB. > > There is one more warning from the common code when I use 256KB pages: > > CC mm/shmem.o > mm/shmem.c: In function 'shmem_truncate_range': > mm/shmem.c:613: warning: division by zero > mm/shmem.c:619: warning: division by zero > mm/shmem.c:644: warning: division by zero > mm/shmem.c: In function 'shmem_unuse_inode': > mm/shmem.c:873: warning: division by zero > > The problem here is that ENTRIES_PER_PAGEPAGE becomes 0x1.0000.0000 > when PAGE_SIZE is 256K. > > How about the following fix ? > > diff --git a/mm/shmem.c b/mm/shmem.c > index 0ed0752..99d7c91 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -57,7 +57,7 @@ > #include <asm/pgtable.h> > > #define ENTRIES_PER_PAGE (PAGE_CACHE_SIZE/sizeof(unsigned long)) > -#define ENTRIES_PER_PAGEPAGE (ENTRIES_PER_PAGE*ENTRIES_PER_PAGE) > +#define ENTRIES_PER_PAGEPAGE ((unsigned long > long)ENTRIES_PER_PAGE*ENTRIES_PER_PAGE) > #define BLOCKS_PER_PAGE (PAGE_CACHE_SIZE/512) > > #define SHMEM_MAX_INDEX (SHMEM_NR_DIRECT + (ENTRIES_PER_PAGEPAGE/2) * > (ENTRIES_PER_PAGE+1)) > @@ -95,7 +95,7 @@ static unsigned long shmem_default_max_inodes(void) > } > #endif > > -static int shmem_getpage(struct inode *inode, unsigned long idx, > +static int shmem_getpage(struct inode *inode, unsigned long long idx, > struct page **pagep, enum sgp_type sgp, int *type); > > static inline struct page *shmem_dir_alloc(gfp_t gfp_mask) > @@ -533,7 +533,7 @@ static void shmem_truncate_range(struct inode *inode, > loff_t start, loff_t end) > int punch_hole; > spinlock_t *needs_lock; > spinlock_t *punch_lock; > - unsigned long upper_limit; > + unsigned long long upper_limit; > > inode->i_ctime = inode->i_mtime = CURRENT_TIME; > idx = (start + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT; > @@ -1175,7 +1175,7 @@ static inline struct mempolicy *shmem_get_sbmpol(struct > shmem_sb_info *sbinfo) > * vm. If we swap it in we mark it dirty since we also free the swap > * entry since a page cannot live in both the swap and page cache > */ > -static int shmem_getpage(struct inode *inode, unsigned long idx, > +static int shmem_getpage(struct inode *inode, unsigned long long idx, > struct page **pagep, enum sgp_type sgp, int *type) > { > struct address_space *mapping = inode->i_mapping; > Looks sane. But to apply this I'd prefer a changelog, a signoff and a grunt from Hugh. Thanks. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev