Srikar, warning. I am going to discuss the things I do not really understand ;) Hopefully someone will correct me if I am wrong. On 10/05, Srikar Dronamraju wrote: > > * Oleg Nesterov <oleg@xxxxxxxxxx> [2011-10-03 18:29:05]: > > > > + page_cache_sync_readahead(mapping, &filp->f_ra, filp, idx, 1); > > > > This schedules the i/o, > > > > > + page = grab_cache_page(mapping, idx); > > > > This finds/locks the page in the page-cache, > > > > > + if (!page) > > > + return -ENOMEM; > > > + > > > + vaddr = kmap_atomic(page); > > > + memcpy(insn, vaddr + off1, nbytes); > > > > What if this page is not PageUptodate() ? > > Since we do a synchronous read ahead, I thought the page would be > populated and upto date. What does this "synchronous" actually mean? First of all, page_cache_sync_readahead() can simply return. Or __do_page_cache_readahead() can "skip" the page if it is already in the page cache. IOW, we do not even know if ->readpage() was called. But even if it was called, afaics (in general) the page will be unlocked and marked Uptodate when I/O completes, not when ->readpage() returns. > would these two lines after grab_cache_page help? > > if (!PageUptodate(page)) > mapping->a_ops->readpage(filp, page); This doesn't look right. At least you need lock_page(). Anyway. Why you can't simply use read_mapping_page() or even kernel_read() ? But the real question is: > > But I am starting to think I simply do not understand this change. > > To the point, I do not underestand why do we need copy_insn() at all. > > We are going to replace this page, can't we save/analyze ->insn later > > when we copy the content of the old page? Most probably I missed > > something simple... Could you please explain? > > But this should not be possible, no? How it can map this vaddr above > > TASK_SIZE ? > > > > get_user_pages(tsk => NULL) is fine. Why else do we need mm->owner ? > > > > > Probably used by the next patches... Say, is_32bit_app(tsk). This > > can use mm->context.ia32_compat (hopefully will be replaced with > > MMF_COMPAT). > > > > We used the tsk struct for checking if the application was 32 bit and > for calling get_user_pages. Since we can pass NULL to get_user_pages and > since we can use mm->context.ia32_compat or MMF_COMPAT, I will remove > get_mm_owner, that way we dont need to be dependent on CONFIG_MM_OWNER. Great! Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>